Preheat oven to 350F. Line an 8 or 9-inch round cake pan with parchment paper and lightly grease it.
In a medium bowl, melt together 1/3 cup of bittersweet/semisweet Chocolate chips and 2 tbsp of Butter. Add in ½ tsp of baking powder, ¼ tsp salt, ½ cup sugar, ½ cup brown sugar, 2 tbsp low fat Sour Cream. Whisk in a egg, a egg white and 1½ tsp of Vanilla Extract. Gently mix in ¾ cup of all purpose flour and 1/3 cup of cocoa powder, mixing until no streaks of flour remain. Batter will be thick. Spread batter into prepared pan.
Bake for about 22 minutes, or until a toothpick inserted into the center comes out with moist crumbs attached. Cool brownies completely in the pan. Store in an airtight container. Makes 12 brownie wedges