Melt butter and baking sqaures in a microwave safe bowl. In the mixing bowl, cream melted butter and chocolate mixture. Add in sugar and vanilla and beat until fluffy, about 2-3 minutes. Add in eggs, beating one at a time. Add flour and cocoa powder and stir just until combined. Fold in chocolate chips.
Fill a muffin tin with muffin liners (I also sprayed my lines with non-stick spray) and fill each liner about 3/4 of the way full. Bake for 20-25 minutes, or until brownie is set. The top with be a bit crunchy and the insides will be fudgey.
Frost if desired and garnish with shaved chocolate.
Fluffy White Frosting
In a small saucepan, stir together sugar, water and cream of tartar over medium heat until the sugar dissolves and mixture is bubbly.
In a mixing bowl, whip the egg whites and vanilla until they form soft peaks. Slowly add the sugar mixture to the egg whites, beating until stiff peaks form, about 7-10 minutes. Frost brownie cupcakes.