1. Break the chocolate into small pieces and melt with butter over hot water in a double boiler.
2. Add egg yolks and orange juice and whisk gently until the mixture is smooth.
3. Let cool in the refrigerator overnight covered by plastic wrap.
4. Scoop a tablespoon of chocolate mixture and roll into truffle ball with your hands.
5. Put in refrigerator again to set.
6. Melt the remaining dark chocolate over hot water and let cool.
7. Coat the cold truffle balls by rolling them rapidly in the melted chocolate using a tea spoon.
8. Place the truffles on a cookies sheet and put in the fridge until the chocolate coating sets.