Preheat oven to 350 degrees F. Butter and flour an oversized, 12-cup muffin tin.
In a large bowl sift together the flour, cocoa powder, baking powder and salt. In a mixer with a whip attachment, cream the butter. Add the sugar and blend well. Add the eggs and vanilla, blending well. Add the dry ingredients and mix on low just until incorporated. Scoop into muffin tins and spread to cover the bottom.
Sauce: Whisk together the ingredients. Pour over and divide among the brownie batter filled muffin tins. Bake for 20 to 25 minutes until set. Serve at room temperature topped with whipped cream.