CHOCOLATE RAINBOW WATERFALL CAKE
1 quantity dark chocolate ganache (recipe below)
2 round (10-inch) cakes (recipe below)
1 quantity buttercream (recipe below)
food colorings: blue, green, red & yellow
2 x 6.8 oz Hershey’s Special Dark Mildly Sweet Chocolate Bar (or a similar large dark chocolate bar)
5 piping bags
1 palette knife or icing smoother

Make the ganache and set it aside to firm up.

Bake the cakes. Turn them out and leave them to cool completely.

Level the cakes. Stack and fill the cakes with ganache. Place the stacked cake on a serving plate.

Make the buttercream. Divide it evenly among 5 different bowls. Color 1 pink, 1 orange, 1 yellow, 1 light green, and 1 light blue. Place each color in a separate piping bag and cut the tip off each to create an opening 3⁄4 inch in diameter.

Starting at the bottom of the cake, pipe a thick line of light blue buttercream around the base. Repeat with light green buttercream, then yellow, orange, and pink. (Don’t be concerned about getting the top line perfect as it will be covered with ganache later.)

Holding a palette knife or an icing smoother vertically, in one smooth motion wipe around the cake, removing any excess frosting. This will blend the colors together. Be sure to wipe your palette knife or icing smoother clean each time you remove the excess frosting.

To prepare the chocolate bar: First you need to make a dagger-shaped extension in one corner of the chocolate bar. This will support the chocolate bar and stop it from falling over. Roughly chop half of one of the dark chocolate bars and melt it in a bowl set over a pan of simmering water, or in the microwave.

Unwrap the second bar of chocolate and place it on a sheet of parchment paper on a flat surface. Pour the melted chocolate over one of the corners of the chocolate bar and then diagonally down, directly onto the parchment paper, to create a dagger shape about 3 inches long and 1 1⁄2 inches wide. 

Set the chocolate aside on a flat surface to cool and harden. (On a very hot day, you might need to put it on a tray in the fridge to cool.) 

Before assembling the cake, check that the ganache is at a spreadable consistency, heating it slightly if too stiff. Spread the ganache over the top of the cake, carefully pushing it to the edges to allow the ganache to drip over the sides of the cake but not form a pool at its base.

With a knife, make a cut in the middle of the cake at least 3 inches deep. Insert the chocolate dagger into the cut so that the chocolate bar appears to be standing up on its corner. Spoon extra ganache around the base of the chocolate bar to make it look like it is melting. Taking a bite out of the top corner is optional!

CHOCOLATE GANACHE
2 1⁄4 cups (14 oz) chocolate chips or disks (milk, dark, or white)
3⁄4 cup (63⁄4 fl oz) heavy cream

Place a medium-size stainless steel bowl over a saucepan of simmering water. Add the chocolate and cream to the bowl and stir continuously with a wooden spoon until the chocolate has just melted and is combined with the cream to a nice glossy finish. Remove the bowl from the heat.

VANILLA CAKE (10-INCH ROUND)
1 3/4 cups butter
1 1/4 cups white chocolate chips
3 cups superfine sugar
2 cups whole milk
2 tsp vanilla extract
2 cups all-purpose flour
2 cups self-rising flour
5 large eggs, lightly beaten

Preheat the oven to 325°F on standard bake (275°–285°F on convection bake, but avoid using convection bake as it causes excessive peaking during baking). Prepare cake pan by greasing with cooking spray. 
Combine butter, white chocolate chips, superfine sugar, milk, and vanilla extract in a large heatproof bowl set over a pot of simmering water until everything has melted together and the sugar is dissolved. Remove from the heat and set aside for 10 minutes to cool down slightly.

In a separate bowl, sift the two flours together, then stir into the melted mixture along with the lightly beaten eggs. Mix gently until the mixture is smooth and free of lumps.

Pour the mixture into the prepared pan, filling it no more than two-thirds full so there is enough room for the cake to bake as it rises. Bake for approximately 1 hour 50 minutes, checking the cake regularly during the last quarter of cooking time, or until a skewer comes out clean when inserted into the cake.

Cool the cake in the pan for 30 minutes, then turn it out onto a wire rack to cool. Once fully cooled, wrap the cake in plastic wrap or place it in an airtight container if you plan to decorate it the following day, or wrap it in aluminum foil followed by plastic wrap and then freeze it.

BUTTERCREAM
9 oz (2 1⁄2 sticks) butter, at room temperature, or 1 1⁄4 cups (9 oz) vegetable shortening
6 cups (1 1⁄2 lb) powdered sugar
2 tbsp milk

Beat butter or vegetable shortening with an electric mixer, using the paddle attachment, until the butter lightens in color or the vegetable shortening softens. Slowly add powdered sugar in small batches (so it doesn’t fly out of the mixing bowl), beating in between until combined. Add milk 1 tablespoon at a time. If using vegetable shortening, you may require more than 2 tablespoons of milk.