Preheat oven to 350 degrees and grease and flour a 13×9 inch baking pan.
Sift together the sugar, flour, cocoa powder, salt, and baking powder in a large mixing bowl. Beat in eggs one at a time on low speed, scraping the bowl occasionally and mixing until smooth.
Fold in chocolate chips.
Transfer batter to a prepared bakin pan and bake for about 30 minutes (until a toothpick inserted comes out clean). Remove from oven and cool on a wire rack. Let cool.
For the Cheesecake layer:
Preheat the oven to 325 degrees.
Blend sugar, cornstarch and cream cheese in a large bowl using an electric mixer. Add lemon juice and vanilla extract , mixing thoroughly. Add eggs one at a time, scraping bowl with each addition. Fold in heavy cream and sour cream.
Spread batter on top of already-baked brownies. Bake 55-60 minutes, until cheesecake is lightly browned and firm.
Cool completely and refrigerated at least one hour before slicing and serving.
Notes
from Disney Files Magazine (not sure of the issue or volume number – working on that)