Line the bottom of a 9 inch springform cake tin with baking parchment. Spray the sides with cooking spray.
Melt the chocolate either in a double boiler or a microwave, and then let the butter melt in the warm chocolate.
Beat the 2 whole eggs and 4 egg yolks with ¼ cup of sugar, then gently add the chocolate mixture, the peppermint extract.
In another bowl, whisk the 4 egg whites until foamy, then gradually add the ½ cup of sugar and whisk until the whites are holding their shape, but not too stiff.
Lighten the chocolate mixture with a dollop of egg whites, and then fold in the rest of the whites. Pour into the prepared tin and bake for 35-40 minutes, or until the cake is risen and cracked, and the center is no longer wobbly. Cool the cake in its tin on a wire rack; the middle will sink as it cools.
When you are ready to eat, place the still tin-bound cake on a cake stand or plate for serving, and carefully remove the cake from its tin. Don’t worry about cracks or rough edges: it’s the crater look we’re going for here.
After the cake has cooled, dust it with powdered sugar, and sprinkle with chopped peppermint candy. Serve with peppermint ice cream!