Preheat your oven to 400˚F.
Butter thoroughly the insides of your muffin tin. Chill in the fridge until your butter has hardened. Repeat two more times.
Mix together the two tablespoons of cocoa powder and the two tablespoons of sugar. After your tin has been buttered three times, coat with cocoa and sugar mixture. Gently tap out the excess coating. Set aside.
Melt the chocolate and butter in a heat-proof bowl set over a small pot of simmering water. Stir occasionally until both have melted and you have a smooth consistency. Remove from the heat and set aside.
Sieve together the flour, 1/2 cup of cocoa powder and icing sugar into a medium sized bowl. Set aside.
Place the eggs and yolks into a large bowl and using an electric hand mixer, beat together. Add 1/3 of the dry ingredients and mix until combined. Continue adding in thirds until all the dry ingredients have been incorporated. Add the melted chocolate and butter and mix together with a spatula.
Divide the batter between your six muffin tins, leaving a 1/4 -1/2 inch border at the top. Bake in the oven for 10 minutes. Your cake should look baked and set on the top and sides. Leave to cool for about 3 minutes and then carefully invert onto a wire rack. Carefully transfer each cake onto a dessert plate. The cakes will not be baked all the way through so handle with care! Dust with icing sugar and enjoy immediately.
I use a standard 6-muffin pan for this recipe: 2 1/2 to 3 inches wide at top and 1 1/2 inches deep. Each will hold approximately 3 1/2 ounces. I find silicone works the best, but if you follow the instructions and butter your tins three times and dust with the cocoa powder and sugar, your cakes should not stick at the end of cooking regardless of the tin you use.