1 1/2 c. unsifted flour
1 1/2 tsp. baking powder
3/4 tsp. salt
6 oz. unsweetened chocolate, chopped
6 oz. semi-sweet chocolate, chopped
1 c. unsalted butter
5 eggs
1 1/4 c. granulated sugar
1 1/2 c. firmly packed dark brown sugar
1 tbsp. vanilla extract
2 1/4 c. walnuts, in lg. pieces

CREAM CHEESE MIXTURE:

12 oz. cream cheese, room temperature
6 tbsp. unsalted butter, room temperature
1 1/2 tsp. vanilla extract
3/4 c. granulated sugar
3 eggs

1. Adjust a rack 1/3 up from the bottom of the oven and preheat the oven to 350 degrees. Prepare a 9 x 13 inch pan as follows: Turn the pan upside down. Carefully center a 17 to 18 inch length of aluminum foil, shiny side down, over the pan. With your hands press down on the sides and corners to shape the foil in the pan and gently press it into place. Lightly butter with melted butter and set aside.

2. Sift together the flour, baking powder and salt; set aside.

3. Place the unsweetened and semi-sweet chocolates and the butter in the top of a large double boiler set over warm water on medium heat, cover and stir occasionally until melted and smooth. Remove the top of the double boiler and set briefly aside.

4. In the large bowl of an electric mixer beat the eggs just to mix. Add both of the sugars and the vanilla; beat only until mixed. On low speed beat in the melted chocolate mixture and then the sifted ingredients, scraping the bowl with a rubber spatula and beating just to incorporate. Remove the bowl from the mixer. Remove and set aside 2 1/4 cups of the mixture.

5. Add about 2/3 of the nuts to the mixture, stirring to mix. Spread the chocolate - nut mixture evenly in the prepared pan and set aside.

6. In a food processor combine the cream cheese and butter, processing until smooth. Add the vanilla, sugar and eggs, beating until smooth. Pour the cheese mixture over the chocolate layer, spreading to the edges of the pan.

7. Stir the remaining chocolate mixture to soften a bit. Spoon in globs over the cheese mixture - it will be very thick and hard to spread. The chocolate layer does not have to cover all of the cheese layer and it does not have to reach the sides of the pan. With a table knife cut through the top chocolate layer into the cheese layer in a zigzag pattern to marbleize slightly. Sprinkle the remaining nuts evenly over the top.

8. Bake in the preheated oven 1 hour and 20 to 25 minutes, or until a cake tester comes out almost clean. Cool in the pan. Then remove the brownies with the foil lining, remove the foil and cut.