DIRECTIONS

Preheat oven to 350°F.

1. Prepare muffin tins with baking spray or line with paper muffin liners. Set aside.
2. Break up or chop chocolate into small pieces. Place pieces in a good size mixing bowl with butter. Pour in boiling water and let stand until melted.  Mix in vanilla and sugar. Whisk in egg yolks, one at a time, beating well after each addition.
3. Meanwhile, in a small bowl or measuring cup, mix together baking soda and sour cream.  Add to batter and whisk in.  Sift the flour into batter. Mix well. 
4. Beat egg whites until stiff (but not dry). Fold them gently but thoroughly into batter.
5. Fill muffin tins approximately 2/3 full. Sprinkle remaining chocolate chips on top.
6. Bake 18 to 20 minutes or until a toothpick comes out clean. Cool 15 minutes on wire racks.