Chocolate Coconut Rum Brownies

Preheat oven to 325 degrees. Butter a 7x11 inch baking dish. Combine both chocolates and butter in the top of a double boiler over simmering water. Melt and stir until smooth. Remove the chocolate mixture from over the simmering water and set aside to cool slightly. Meanwhile, beat together sugar and 3 eggs until light and fluffy. Mix in coconut, flour, sour cream, vanilla, rum and baking powder. Stir in the melted chocolate mixture. Beat egg whites to stiff peaks in a medium bowl. Fold the beaten whites into the batter. Spread the batter evenly in the prepared dish. Bake brownies about 40 minutes until a toothpick comes out clean. Transfer dish to a rack and cool brownies completely. Cut brownies into squares and serve.