Berry Swirl Cheesecake Bars with Sourdough Sugar Cookie Crust

Preheat the oven to 325°F (163°C).
Line a 9x9-inch baking pan with parchment paper, leaving enough overhang on two sides to easily lift the cheesecake bars out after chilling.

In a medium bowl, whisk together the flour, baking powder, and salt. Set aside.
In a large mixing bowl, beat the softened butter and granulated sugar together until light and fluffy, about 2-3 minutes.
Mix in the egg until fully incorporated.
Add the sourdough discard and vanilla extract, mixing until smooth.
Gradually add the dry ingredients and mix just until a soft dough forms. Avoid overmixing.
Transfer the dough to the prepared baking pan. Using lightly floured hands or an offset spatula, gently press the dough into an even layer, making sure it reaches all four corners.
Bake for 18-20 minutes, or until the edges are lightly golden and the center appears mostly set. The crust does not need to be completely browned since it will continue baking with the cheesecake.
Remove from the oven and set aside while preparing the filling.

While the crust bakes, combine the blueberries, diced strawberries, raspberries, granulated sugar, and cornstarch in a small saucepan.
Cook over medium heat, stirring frequently, until the berries begin to break down and release their juices. Continue cooking for about 8-10 minutes until the mixture thickens enough to coat the back of a spoon.
For a smoother swirl, use an immersion blender or the back of a spoon while cooking.
Remove from the heat and allow the berry sauce to cool slightly before assembling the cheesecake.

In a large mixing bowl, beat the softened cream cheese until completely smooth with no lumps.
Add the sugar and mix until creamy.
Mix in the Greek yogurt, vanilla extract, and salt.
Add the eggs one at a time, mixing on low speed after each addition until just combined.
Finally, mix in the flour until incorporated. Do not overmix, as too much air can cause the cheesecake to crack.

Pour the cheesecake filling over the partially baked sugar cookie crust and spread it into an even layer.
Using a spoon, drop small dollops of the berry sauce evenly across the top of the cheesecake. You'll have extra sauce. Save this to top your cheesecake with when serving (it's incredible with the sauce and some whipped topping!).
Using the tip of a butter knife, gently drag the knife through the berry dollops in smooth figure-eight or S-shaped motions. Rotate the pan as needed and continue swirling until you have a beautiful marbled pattern. Be careful not to overmix, or the colors will blend together instead of creating distinct swirls.

Bake at 325°F (163°C) for 40-45 minutes, or until the edges are set and the center still has a slight jiggle when gently shaken.
Avoid overbaking, as the cheesecake will continue setting while it cools.

Turn off the oven and crack the oven door open several inches.
Allow the cheesecake to cool slowly in the oven for about 45-60 minutes. This gradual cooling helps reduce the chances of cracking.
Transfer the pan to the counter and let it cool completely to room temperature.
Cover the pan tightly and refrigerate for at least 4-5 hours, though overnight chilling is highly recommended for the cleanest slices and best flavor.

Use the parchment paper overhang to lift the chilled cheesecake from the pan.
Slice into bars using a sharp knife, wiping the blade clean between each cut for neat slices.
Serve with the reserved berry sauce spooned over each bar and a dollop of whipped cream or whipped topping, if desired.