You will need:
2 silicone mats
Marzipan or filling for the sugar tubes.
Skin colored food dye
Butter cream frosting (fresh or pre-made)
Alton Brown's Red Velvet Cake:
5 1/2 ounces all-purpose flour
4 ounces cake flour
1/2 ounce natural cocoa
1 teaspoon baking soda
1/2 teaspoon kosher salt
1 cup low-fat buttermilk, room temperature
1 fluid ounce red liquid food coloring
1 tablespoon white vinegar
1 teaspoon vanilla extract
10 1/2 ounces dark brown sugar
4 ounces unsalted butter, room temperature
2 whole eggs, room temperature
2 c. water
1 c. corn syrup
3 1/2 c. white sugar
1/4 tsp. cream of tartar
Step 1. Make your favorite red velvet cake recipe (I like Alton Brown's) or you can use a box mix in an 8x13 pan. I made a larger cake so I doubled the recipe.
Step 2. Once you have started this step, you will be limited on time to form the bones of the arm before the candy sets. Make sure you have time available to complete this step from start to finish. Mix the items from the sugar bone recipe above in a medium saucepan to the hard crack stage (300° F - 310° F). Once you have reached the correct temperature you will need to pour half the candy onto a silicone mat. Using potholder gloves roll the silicone mat so the sugar meets to form a tube. Do not overlap the silicone as it will stick and cause the tube to break. Repeat on the second silicone mat. Let these cool.
Step 3. Cut the cooled Red Velvet Cake into the shape of an arm (think teardrop shape). You will need to cut channels into the middle of the cake large enough for the sugar tubes to fit. Keep all scraps; you will need them for the upcoming steps.
Step 4. I used marzipan to fill my sugar tubes because it reminded me of bone marrow, but you can use any dense candy which does not contain a lot of water. I purchased mine from an ethnic store near me, but there are many recipes online should you decide to make it. Warm the marzipan by gently kneading it, and then stuff it into the sugar tubes.
Step 5. Place the stuffed sugar tubes into the channels of your red velvet cake. Use the scrap cake pieces and the second 8x13 cake to form the rest of the arm and a hand. For an extra gross effect, I left the "severed" part of my arm a bit ragged with the bones protruding.
Step 6. Mix the skin colored food dye into the fondant and roll it into a sheet. I used a damp kitchen towel to texture my arm to give it a slight realistic look. Lightly frost the arm and hand with the butter cream icing, then gently lay the fondant over it. The arm will look lumpy so smooth the fondant as much as possible.
Step 7. Decorate as you see fit! I cut surface slices into my cake to show the "muscle" underneath, used red food gel to make bloody streaks. Let your imagination run wild!