1

Preheat oven to 350 degrees F. Lightly grease 13x9" pan.

2

Place unsweetened chocolate and semi-sweet chocolate and butter in medium microwavable bowl. Microwave on high for 2 minutes, or until butter is melted; stir until chocolate is completely melted. Cool to room temperature.

3

Combine flour, salt and baking powder in small bowl. Set aside.

4

Beat sugar, eggs and vanilla in a large bowl with an electric mixer at medium speed until slightly thickened. Beat in chocolate mixture until well-combined. Add flour mixture; beat at low speed until blended. Add sour cream; beat at low speed until combined. Stir in chocolate chips.

5

Spread mixture evenly into prepared pan. Bake 20-25 minutes, or until toothpick inserted in center comes out almost clean. Cool brownies completely in pan on wire rack before cutting into squares.

6

Place powdered sugar in fine-mesh strainer and sprinkle over brownies.