Introduction: Watermelon Slices Cake With Buttercream Frosting

Picture of Watermelon Slices Cake With Buttercream Frosting

This cake is one of my favorites to make.
I’ve made it several times before, and I have gotten wonderful feedback of how “beautiful” it looks and how wonderful it tastes.  Little do the connoisseurs know how EASY it was to make too!

I wrote this instructable for two purposes.  To describe and show how to make the Best Buttercream Frosting ever and how to make and decorate the Watermelon Slices Cake.

This particular cake I made for my son’s schools cake walk.  I’ve made it before for work picnics, bake sales, and summer family gatherings.

If you’re here to make the Best Buttercream Frosting ever, check out Steps 1 and 2.

The whole cake can be made in one evening, if you purchase pre-made white frosting.  I put the estimated times it takes to make the components of the cake in each step.

The original recipe came from a book I’ve had for years, and I was fortunate to find the recipe on the internet for you all to see.  It’s a Betty Crocker recipe and can be found here: Watermelon Cake.

Please note that this cake doesn’t taste anything like a watermelon (unless you add watermelon jell-o flavoring.)  It just looks like a slice of one.  Enjoy!

Step 1: Ingredients and Tools

Picture of Ingredients and Tools
Buttercream Frosting Ingredients:
• 1 cup unsalted butter, softened
• 1 cup white frosting
• 4 tablespoons all-purpose flour
• 1 cup milk
• 1 teaspoon vanilla extract

For decorating you will also need:
• red food coloring
• green food coloring
• my friend, Wax Paper

Buttercream Frosting Tools:
• Saucepan
• Spoon to stir (I used a wooden one)
• Measuring cups/spoons
• Bowl to mix it in
• Bowl to cool the frosting mixture in
• Electric Mixer
• Spatula

Optional Frosting Choice: 1 container of white frosting (if you don’t make your own)

Cake Ingredients:
• 1/2 cup plus 2 tablespoons miniature semisweet chocolate chips
• 1 box white cake mix
• Water, vegetable oil and egg whites called for on cake mix box
• 1 package (0.13 oz) cherry-flavored or other red-colored unsweetened soft drink mix  OR 1 package (3 oz) watermelon flavored sugar-free jell-o powder
• Optional: 2/3 cup green jelly beans (not pictured because I don’t use them)

Standard Cake Baking Tools: Bowl to mix cake, electric mixer, two 8” or 9” circle cake pans, and oil or cooking spray to grease the pans.

Because this was a cake-walk cake that we donated, I also purchased a dollar store cake carrier.

Step 2: Prepare the Buttercream Frosting

Picture of Prepare the Buttercream Frosting

The original recipe for this frosting is here.

RECIPE TIP: Always read the reviews for an online recipe! 
One thing about this frosting recipe is that the reviews had so much information.  Most of the directions I have listed below are from following the comments from the reviews.

I made this frosting the day before I made and frosted the cake.  The total time commitment was about two hours.

Allow the butter to soften.  For me, this means leaving it on the counter for an hour or two.  You can also microwave it for 15-20 seconds, but you DON’T want melted butter, just softened.

While waiting for the butter to soften, you can make the flour-milk mixture.
Whisk together the milk and two tablespoons of flour until smooth.

Pour the milk and flour mixture into a saucepan and heat on medium heat, stirring constantly for 3-4 minutes, until thickened.

Remove from heat and transfer to a dish for the mixture to cool in to room temperature.  I spread the mixture out over the bowl so that the surface area was greater and the mixture would cool faster.
I waited a little over 30-minutes and in my house, room temperature is about 80-degrees F.

After the milk-flour mixture has cooled, I mixed the softened butter with the sugar.  To reduce the grit from the sugar, I used the electric mixer to mix the butter and sugar for 15 minutes on the low setting, scraping down the sides every once in a while.

After whipping the butter/sugar mix for 15-minutes, add the flour-milk mixture and beat both mixtures together on high speed for about 2 minutes.
Add the vanilla extract and beat on high speed for 2 more minutes, or until thoroughly combined.

The recipe states to keep it in the refrigerator for ½-hour or until a spreadable consistency.

As I made this frosting a day before making the cake, I put the frosting in a container and left in the fridge until the next day to add the food coloring.

See step 4 for adding color to the frosting.

Step 3: Mix and Bake the Cake

Picture of Mix and Bake the Cake

The total time commitment for making the cake (and letting it cool to frost) is about one-hour.

Heat oven to 350°F (325°F for dark or nonstick pans).

Grease or spray two 8- or 9-inch round cake pans.

In large bowl, beat cake mix, the water, oil, egg whites and drink mix (or jello mix) with electric mixer on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally.
To see how I separate my egg whites, as I don't have an egg separator, click on another instructable where I show how to do that here.

Recipe Tip: The watermelon jell-o mix will make the cake taste like a watermelon-flavored cake, whereas the drink mix will only color the cake, not make it flavored.  (I have never tried the watermelon jello mix, as it does not sound appealing to me….)

Fold in the 1/2 cup chocolate chips. Pour into bottom-greased pans.

Bake and cool as directed on box for 8- or 9-inch rounds.

Test the cake if it's done by pricking a toothpick into the thickest part of the cake.  If the toothpick comes out clean (meaning not with cake mix on it,) EXCEPT for a chocolate residue, then the cake is done.

Allow the cakes to sit in their baking pans for ten (10) minutes before transferring to a cooling rack.

I place my cake rounds on parchment paper on top of my cooling rack.  That way, the little cooling rack squares don’t show up on the cakes as much as they would if they sat directly on the rack.

Allow the cakes to cool completely before frosting.  That may be an additional 20 to 30-minutes or so.

Step 4: Prepare the Frosting

Picture of Prepare the Frosting

While the cake is baking, I let my frosting sit on the counter to come to a spread-able consistency.  It took about ½-hour in my home.

Once the frosting is spreadable, in small bowl, stir 1 cup of the frosting with 15 to 20 drops green food coloring.

Stir 15 to 20 drops red food coloring into remaining frosting.

Step 5: Assemble and Decorate

Picture of Assemble and Decorate

It takes me about 20 minutes to decorate the cake.  It would take longer if you choose to use jelly beans.
Let me introduce my friend, waxed paper here.

I am in no way a good cake decorator and I do not have the tools to prove it.  My friend, waxed paper, makes it so I can decorate the cake on the same plate I am going to serve it on and not make a huge mess.  In this case, I bought a dollar store cake carrier to give the cake away to my son’s school’s cake walk.

Roll out a piece of waxed paper, enough to cover the plate.  Begin by cutting the piece in half and then each half again so you have four pieces.

Place the waxed paper on the serving plate/decorating tray, so that there is an open area in the center of the plate/tray. 

Place the cake, rounded top down, onto the tray.  Test each piece of wax paper now by tugging on it slightly, to ensure that it will slide out from under the cake after it has been decorated.

Optional: If the cake layer is too rounded on top after baking, slice off the center hump to make flat.  Continue to place that cut side on the plate before decorating.

Place a layer of red (or pink) frosting on top of the bottom layer of the cake.  In order not to mix the colors of the outside frosting with the layer of frosting (as they are two different colors in this case) stop short of frosting around the edge of the bottom layer.  I left about ¼” around the outside edge.

Place the second cake, rounded side up, on top of the bottom layer of the cake.

Frost sides of cakes with green frosting.  At this point, I’m not so concerned with the look, just getting the frosting on the majority of the cake.

Frost the top of the cake with the pink frosting, using a spatula to meet the edges of the top layer of the cake.

I usually finish the cake with a butter knife, adding a dab of green frosting here and there to completely cover the sides as needed.  I also take my spatula and in larger sweeping movements, stroke the top of the cake back and forth to get a more finished look.

Sprinkle two tablespoons (or so) of miniature chocolate chips on the top of the cake.

Optional: Not shown - press green jelly beans into green frosting on side.  There is a good photo of this on the Betty Crocker website.  (I have done this, and was not impressed.  I saw more people take the jelly beans off than eat them with the cake.)

Step 6: Presentation

Picture of Presentation

Firmly grab a hold of one piece of waxed paper at a time and slowly tug to remove from the bottom layer.  Hopefully, the tray or plate will be clean as mine was.  Repeat this process with each piece of waxed paper.

The Betty Crocker website suggests one way to present the cake, which is not shown here.  As mine was for a cake walk, I didn’t want to cut into it.
If desired, cut cakes crosswise in half and arrange "slices" randomly on tray. To serve, cut into wedges.

I placed the cake carrier lid on top, typed up a donation card, and stuck it on a piece of scrapbooking paper.  I then used removable double sided tape, to stick the donation card onto the outside lid.

Because I made my own butter-cream frosting, I refrigerated the cake until the day of the cake walk.

Should I have used store-bought frosting, I would probably have stored the cake “loosely covered” as suggested on the Betty Crocker website.

I hope the recipients enjoyed it as much as I loved making it and I really hope you will give this recipe a try!

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Bio: I crochet and do crafts. Oh and I also work full time and have a family to take care of. I'm on here because ... More »
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