Preheat oven 325 and line 8x8 pan with nonstick foil.
Microwave cream cheese until soft, 20 to 30 seconds. Add sour cream, sugar, and flour and whisk to combine. Set aside.
Microwave butter and chocolate until melted.
In a bowl, whisk sugar, eggs, and vanilla together. Add the melted chocolate mixture (do not clean bowl) and whisk until incorporated.
Add flour, salt and baking powder. Fold to combine.
Transfer 1/2 cup batter to bowl used to melt chocolate. Spread remaining batter in prepared pan. Spread cream cheese filling evenly over batter.
Microwave bowl of reserved batter until warm and dollop over cheesecake layer.
Swirl with a knife.
Bake approx 40 mins.
Let cool, chill and cut.