Preheat oven to 325 degrees Fahrenheit. Line a 9 inch square baking pan with parchment paper.
Make the blondies:
In a large bowl, cream together the butter, sugar and brown sugar until light and fluffy.
Add in the eggs and vanilla and mix well.
Add the flour, baking powder and salt and mix until just combined.
Make the cheesecake:
In a second bowl, beat together the cream cheese, sugar, sour cream, egg and vanilla until smooth and creamy.
Stir in the blueberries.
Place half of the blondie batter into the prepared pan and smooth out to cover the bottom of the pan.
Place spoonfuls of the cheesecake batter on top of the blondie batter, but do not spread out.
Place spoonfuls of the remaining blondie batter around the cheesecake batter. If necessary, smooth out the top of the batters so that they are mostly even.
Bake at 325 degrees for 40-50 minutes or until a toothpick inserted into the middle comes out mostly clean, or with just a few moist crumbs. The top will be a light golden brown color.
Allow to cool to room temperature and the refrigerate until chilled.
Slice into 16 squares.
Store tightly covered in the refrigerator.
The calories shown are based on the bars being cut into 16 pieces, with 1 serving being 1 bar. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate. **We are not dietitians and recommend you seek a nutritionist for exact nutritional information. The information in the nutrition box are calculated through a program and there is room for error. If you need an accurate count, I recommend running the ingredients through your favorite nutrition calculator.**