Preheat the oven to 350°F. Lightly coat a 9 x 9 inch baking pan with non-stick spray, line with parchment paper, and then coat the parchment paper with non-stick spray. Set aside.
To Make the Brownie Layer: In a medium-sized mixing bowl, use a whisk to sift together flour, cocoa powder, salt, baking powder and espresso powder until completely combined.
Using an electric mixer, cream together butter and sugar on medium-high speed until light and fluffy. To the creamed mixture, add milk, vanilla and eggs. Beat together on low speed until combined. It won't be completely smooth.
While beating on medium speed, gradually add sifted dry ingredients mixing just until combined. The batter will be thick. Scrape down the sides of the bowl as needed. Measure out ⅓ cup of batter and set aside for the swirl. Fold chocolate chips into the remaining brownie batter then spread evenly in prepared pan.
To Prepare the Cheesecake Layer: In a separate bowl, use an electric mixer to beat together sugar, and cream cheese and vanilla for 2 minutes or until creamy. Add the sour cream and egg, mixing on low until smooth. Pour the cream cheese mixture on top of the brownie layer and spread evenly using an offset or rubber spatula.
To Add the Brownie Swirl: Dollop about 2 tsp of reserved batter randomly over cheesecake layer. Use a skewer or the tip of a sharp knife to create swirls. Don't go too deep, swirl the cheesecake layer only.
Bake for 35-40 minutes or until the edge of the cheesecake layer is set but the center jiggles slightly. Remove from the oven and cool on a wire rack for 30 minutes.
Place into the fridge and chill in the pan for 2 hours OR until fully set.
Cut into 9 servings and enjoy. Store leftovers chilled.