For the cake:
1/2 cup (1 stick) butter
1 3/4 cup sugar
3 cups sifted all purpose flour
4 teaspoons baking powder
1/4 teaspoons salt
1 cup milk
5 eggs (separated)
For the frosting:
1/3 cup softened butter
1/4 teaspoon salt
1 teaspoon vanilla extract (or whatever)
1 pound (about 3 1/2 cups) sifted confectioners sugar
2 egg whites (unbeaten)
1 Tablespoon milk (about)
Step 1: Mixing the Batter
Grease and lightly flour two 8 inch pans.
Cream butter and sugar well. Add dry ingredients, sifted together, alternating with milk and egg yolks, beginning with dry and ending with dry.
Beat the egg white until they hold stiff peaks and fold them into batter. (This step isn't completely necessary as when I added the food coloring I flattened all that fluffy goodness. I suppose you could separate the batter, then color it and add an equal amount of egg whites, but I went another way as you shall see)
Step 2: Coloring the Batter
Find a glass or container that will fit a ziplock sandwich bag. Flip the rim outward. Separate the batter equally, about 1/2 to 1 cup should work. Add food coloring, close, and knead to mix.
Again, this takes away from the lightness of the cake, but doesn't bother the flavor one bit.
Do this however many times and colors you desire. I fudged on the purple so had only 5 instead of six. For yellow, I just left the batter alone, using only 4 bags for the color.
Step 3: Filling the Pans
Using about a tablespoons worth of batter, start with your darkest color and work through the rainbow, over and over again. The batter will spread out on its own.
Step 4: Baking
Bake until a toothpick stuck in the middle comes out clean.
Step 5: Shaping
Using your pan as a guide, place a piece of wax paper down, trace the pan, then cut it out.
Fold the resulting circle into quarters, nip a dip in the middle then round the edges . It will look a little like a heart. Unfold and place the template on top of the cakes.
I stacked mine, thinking of doing just one two layered cake, but wound up making two single layers. (The natives were restless so I did a quicky topping.)
Using a steak knife cut the rough shape. You can fine tune it afterward.
Step 6: Icing
The first is simply powdered sugar sprinkled on top along with some green sugar sprinkles.
The second is a butter cream frosting recipe my grandmother used.
You cream the butter, salt and flavoring until light and fluffy. Then add the sugar and egg alternately, beating after each addition. Add milk until smooth. It makes about 2 1/4 cups.
Add green food coloring of course.
I piped mine but it's not necessary. I was just attempting my grandmothers technique. I think if I had chilled the frosting longer that it would have come out a bit sharper.
Cut in and enjoy the good luck rainbow inside the shamrock!!