Preheat oven to 350 degrees. Line the bottom of two 12 cup muffin pans with paper liners.
Melt chocolate in a double boiler over simmering water. In a bowl, stir baking soda into the boiling water, stir this mixture into chocalate. Let cool just a little.
Mix cream, butter and sugar, with electric mixer until mix is pale yellow. Add eggs, one at a time, continue to mix thoroughly. Add flour & buttermilk, alternating small amounts of each. Blend well.
Add melted chocolate and vanilla to the batter, stir well. Pour batter into paper cups. Bake until cake tester comes out clean when inserted into center of cupcake, about a half an hour. Remove from oven, and allow to cool briefly in muffin tin. Remove from muffin tin, place on wire rack to finish cooling. Ice and serve.
