The oven is heated to 190 C. Prepare 14 muffin forms, which put paper cups. The butter was stirred with sugar. Add the eggs one at a time and the mixture was stirred until absorb better. Pour the yogurt, orange juice and orange peel and stir again. Sift the flour with the baking powder and parts added to the egg mixture. Finally add the chocolate pieces. Pour into paper cups. Cupcakes bake 25-30 minutes. Check with a wooden stick, which pinned in the center of the cake should come out dry. After removing from the oven muffins leave for 5 minutes and then released from the mold. Optional can be covered with chocolate and decorated with candied orange peels.