Preheat oven to 350F. Grease an 8x8" square metal baking pan. Brownie Layer - Beat together melted butter, sugar, and vanilla, then beat in eggs one at a time. Combine dry ingredients and then gradually stir into butter mixture with a wooden spoon. In separate bowl, beat together cheesecake batter ingredients. Spread about 2/3 of chocolate batter into prepared pan, and spoon cheesecake batter over. Dollop remaining brownie batter over cheesecake batter. Swirl the batters together by running a butter knife back and forth through the pan. Bake for 40 minutes, or until center is set. Cool completely on wire rack and chill before cutting and serving.