Preheat the oven to 350 degrees. Line the inside of an 8 inch square metal pan with nonstick foil.
Mix the flour, cocoa, baking powder, and salt together; set aside.
In a large saucepan set over medium low heat, carefully melt the chocolate and butter together, stirring often so that you don't scorch the chocolate. Alternatively, you may do this in the top of a double boiler or in a bowl set over simmering water.
Remove chocolate from heat and let cool for 3 minutes. Stir in the sour cream, syrup and vanilla, followed by the egg and egg white and sugar.
With a heavy duty scraper, fold in the flour mixture.
Transfer mixture to the pan and spread it flat. Bake on center rack for 20 to 25 minutes.
Let brownies cool completely in pan set on a wire rack. Using foil as a handle, lift from pan and cut into squares