In small bowl, combine flour, baking powder and salt; set aside. In medium microwave safe bowl, melt butter and chopped chocolate. Stir in sugar, eggs, and vanilla; mix well. Add flour mixture; mix until just combined. Spread half of the chocolate batter in the pan; alternately drop spoonfuls of cheesecake batter and chocolate batter into pan. Swirl the two batters together with a knife to create a marbled effect.