This is the cake I used for the Pokemon cake a few months ago. The recipe is from Gluten-Free Goddess, with some tweaks because I didn't have everything on hand (like organic light brown sugar swapped to regular brown sugar). I'm posting it on the good authority of the pantees that it actually tastes good - I had to leave the party early so I didn't actually get to eat any of it!
FLOURLESS CHOCOLATE CAKE
450g dark chocolate
1 cup brown sugar
1/2 cup white sugar
250g unsalted butter
2 tbsp cocoa powder
8 large eggs
1 tbsp vanilla extract
1. Preheat oven to 180C. Line a pan with greaseproof paper.
2. Melt the chocolate and mix with sugar until combined. Add the butter and cocoa powder and mix.
3. Add the eggs and vanilla, and mix until smooth and creamy.
4. Pour batter into pan and bake until cooked through (roughly 45min-1hr if I remember correctly).