Gummy Bear Layer Cake

Ingredients:

3 cups (about 385g) plain/all-purpose flour
2 &1/2 cups (about 560g) sugar (I used caster/superfine but white/granulated is fine too)
1 tbsp baking powder
2 tsp baking/bicarb soda
1 tsp salt
1 & 1/2 cups unsweetened cocoa powder, preferably Dutch-process
340g (3 sticks) butter, melted
1 & 1/2 cups (about 360ml) buttermilk
4 large egg
4 large egg whites

Directions:

Preheat oven to 180°C (350°F). Grease and line three 18-20cm round cake tins (if you have taller cake tins you can do this in two tins, don't risk it if your tins are shallow like mine as the batter may overflow). Line a standard cupcake tray with papers. In a large mixing bowl, combine flour, sugar, baking powder, bicarb soda, and salt; set aside. With an electric mixer, combine cocoa and 3/4 cup hot water until a thick paste forms (this process intensifies the chocolate flavor). Add butter, buttermilk, eggs, and egg whites; beat until combined. Whisk in flour mixture until smooth. Pour mixture into tins, distributing to make 5 layers (2/5 in two of the tins and 1/5 in the 3rd, or if using two tall tins; 3/5 in one and 2/5 in the other). Bake until a skewer inserted in the center of cake comes out clean, about 45-60 minutes.Cool in tin for 10 minutes then carefully remove from tin and cool completely on a wire rack. You can chill the cakes at this point to make them easier to cut. Using a long serrated knife, cut cakes into 5 even layers and trim off any doming that may have occurred during baking. (I used this trick to help my cakes bake more evenly)

For the icing:

(It sounds like a lot of butter and sugar but you need a lot to cover all 5 layers. Feel free to halve the amounts for a smaller cake)
500g (about 4 1/3 sticks) salted butter, softened
500g (about 4 cups) icing/confectioner's sugar, sifted
1 tsp pure vanilla extract
2-3 tbsp milk

Optional: 

Green, yellow, red food coloring
375g (3 & 1/3 sticks) salted butter, softened
375 (3 cups) icing/confectioner's sugar, sifted
1/2 tsp pure vanilla extract
1-2 tbsp milk
4 packs (700g) of gummy bear candies

Directions:

To fill the cake layers and crumb coat the cake, place the 500g of butter in a large mixing bowl and beat until light and fluffy. Gradually add 500g sifted icing sugar while beating on low speed until combined, then add vanilla extract and beat on high until fluffy. Add milk 1 tbsp at a time while beating on high until you achieve desired icing consistency. Icing should be very fluffy and light in color, easy to spread but stiff enough to hold its shape. Split mixture into 5 equal portions. Add food coloring to four of the portions, green, yellow, orange and red. Sandwich colored icing between the 5 layers of cake. Use the remaining icing to crumb coat the outside of your cake. Chill in fridge for at least an hour, can be left overnight.

Prepare more icing using the remaining ingredients and repeating the steps above, without adding food coloring. Using a spatula, spread icing smoothly over the top of the crumb coat. Decorate cake with gummy bears. Serve immediately or store in an airtight container until ready to serve.