Microwave the chocolate in small pieces with the butter for 3 minutes on 1/2 power in a glass bowl.
Take out of the microwave and stir until smooth.
Add the egg yolks slowly while stirring.
Add the sugar.
Stir until all ingredients are incorporated and refrigerate for a couple of hours.
Take out of the refrigerator and form roughly teaspoon sized balls.
Dust them with the cocoa powder.
Keep the truffles frozen until ready to use.
The recipe will make 35-40 truffles. Enough for a crowd.