Step 2: Mix 1 (12 ounce) can evaporated milk and enough whole milk to make 2 3/4 cups. Set aside. In a large mixing bowl, combine 2 boxes of cake mix, 2 sticks (16 tablespoons) butter, 8 eggs, 2 teaspoons vanilla and half of the evaporated milk-whole milk mixture. Stir very slowly to blend. With an electric mixer, mix on low speed for approximately 5 minutes.
Step 3: Add the rest of the milk mixture and blend on medium-high speed for 10 minutes or until the batter has a smooth cake consistency. (In 10 minutes, the batter will form ribbons).
Step 4: Spray 10 (9-inch) cake pans. Spread 1 cup of cake batter into each of the pans evenly. Bake each cake for 10 minutes (they will slightly brown and pull away from sides of pan). Repeat this until you have 10 layers.
Step 5: To make the icing: In a large saucepan, melt 2 sticks (16 tablespoons) butter. Take pan off the heat and stir in 2 cans evaporated milk. Whisk in 8 heaping tablespoons unsweetened cocoa until smooth. Return pan to heat and cook for approximately 10 minutes. Do not boil or scorch.
Step 6: Remove from heat and whisk in 2 pounds confectioners' sugar slowly. Return icing to low heat and cook slowly, stirring often, until icing has thickened and will stick to back of spoon or whisk (it will form a ribbon when you drizzle a spoonful onto mixture while cooking). This will take at least 45 minutes to 1 hour.
Step 7: To assemble the cake, spread 1 slightly cooled cake layer with cooled frosting. Add next layer and repeat the process until the 10th layer. Finish by frosting cake top and sides.