Melt chocolate and 3 tablespoons butter in a small saucepan over very low heat, stirring constantly (or use a double boiler). Set aside to cool while making the cream cheese mixture and brownie batter.

Using an electric mixer, mix 2 tablespoons butter with cream cheese, until creamy. Gradually add 1/4 cup sugar, beating well. Blend in one egg, 1 tablespoon flour and 1/2 teaspoon vanilla. Set aside.

In a separate bowl, using an electric mixer beat 2 eggs until thick and light in color. Gradually add remaining 3/4 cup sugar, beating until thick. Add baking powder, salt and 1/2 cup flour.

Blend in cooled chocolate mixture, nuts and 1 teaspoon of vanilla.

Spread about half the chocolate batter in a greased and floured 9 x 9" square baking pan. Add cheese mixture, spreading evenly. Top with tablespoons of remaining chocolate batter. Zigzag a spatula or butter knife through the batter to marble.

Bake at 350 degrees for 35-40 minutes or until top springs back when touched lightly in center, or when toothpick comes out clean. Cool and cut into bars. Store in refrigerator.