1/4 cup rainbow sprinkles (NOT the round sprinkles - the colour will bleed into the cake batter! Use the flat, confetti-like sprinkles or the long 'jimmies')
2 cups vanilla buttercream (recipe here)
Neon food colouring
Bake the cake: Combine the flour, baking powder and salt in a bowl. In a separate bowl, beat the butter with an electric mixer until pale and fluffy. Add the sugar and mix until combined. Add the vanilla extract and eggs and beat until combined. Add the dry ingredients in 2 additions, alternating with the milk. Then add the sprinkles and mix until just combined. Divide into 2 greased 9-inch round cake pans and bake at 350F for 20-25 minutes, or until fully cooked. Cool completely.
To assemble, cut the cakes into clean circles and trim the tops and bottoms, to create even surfaces. Then slice each cake in half to create a total of 4 layers. Place half of the buttercream in a bowl, then divide the remaining buttercream into 3 bowls. Dye them any neon colours of your choice.
Place one layer of cake on a serving tray of your choice and spread one bowl of the neon buttercream over the entire surface. Repeat with another layer of cake and neon buttercream, until you reach the final layer of cake. Then cover the entire surface of the cake with the white buttercream.
To attach the gummy bears, place 2 red gummy bears at the base of the cake, followed by 2 orange, 2 yellow, 2 green and 2 clear gummy bears. Repeat until both ends of the gummy bear chain meet. Repeat directly above the gummy bears, but shift the position slightly, so that the first red gummy bear on the second level is positioned between the two red gummy bears on the first level. Repeat until the entire cake is covered. Place more gummy bears onto the center of the cake and serve!