Marbled Chocolate Brownies 'Hmmmm Good'

**************Prep time 15 minutes ---- Baking time : 30 minutes*******
1 bar (4 ounces) bittersweet baking chocolate
1/2 cup (1 stick) butter
2 tablespoons cocoa powder
1 1/4 cups sugar
1/4 teaspoon salt
3 eggs
1 teaspoon vanilla extract
1 cup all-purpose flour
1/2 teaspoon baking powder
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*************TOPPING
1 cup semisweet chocolate baking chips
1 cup white chocolate baking chips
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1) Prehaet oven to 350*F , line a 9-inch square baking pan with aluminum foil , making sure some of the foil hangs over the sides . Spray the foil with nonstick cooking spray .
2) Chop the bittersweet chocolate into small pieces . Place the chocolate , butter and coca powder in a microwave-safe bowl . Microwave on high until the chocolate and butter are melted . Stir to combine and set aside.
3) Place the sugar and salt in a medium bowl . Add the chocolate mixture , stirring to combine . Add the eggs , one at a time , stirring after each addition . Stie in the vanilla . Sift in the flour and baking powder ; mix well.
4) Spread the batter in the prepared baking pan . Bake brownies for 30 minutes . Remove the pan from the oven.
5) Sprinkle the chocolate chips over the brownies . Return brownies to oven for 1 minute . Remove from oven ; allow the pan to sit for a 1 minute . Lift the brownies out of the pan (using the foil as handles). Spread the chocolate chips over the brownies for a marbled effect . Let cool completely before cutting into bars .