1-Step 1: Prepare Your Baking Setup Preheat your oven to 350°F. This temperature ensures even baking throughout without burning the crust. Grease a 9×13-inch baking pan generously with butter or cooking spray. For easier removal and cleanup, you can also line the pan with parchment paper, leaving an overhang on the sides to lift the bars out after cooling.

2-Step 2: Make the Crumb Mixture In a food processor, combine the flour, sugar, and salt. Pulse a few times to blend the dry ingredients evenly. Add the cold butter cubes and process until the mixture becomes crumbly and starts to clump together when pressed. This should take about 30-45 seconds of processing. The mixture should look like coarse sand with some larger butter pieces visible. If you don’t have a food processor, you can use a pastry blender or two forks to cut the butter into the dry ingredients until the same consistency is achieved.

3-Step 3: Reserve Topping and Press Crust Measure out and reserve 1 1/2 cups of the crumb mixture for the topping. Set this aside in a separate bowl. Press the remaining crumb mixture firmly and evenly into the bottom of your prepared 9×13-inch pan. Use the bottom of a measuring cup or your hands to create a compact, even layer. This pressed layer will become your bottom crust after baking.

4-Step 4: Par-Bake the Crust Place the pan in the preheated oven and bake the crust for 12-15 minutes until it turns a light golden brown color. This partial baking ensures the crust won’t become soggy when the fruit filling is added. Remove the pan from the oven and let it cool for at least 10 minutes before adding the filling. This cooling period prevents the egg-based filling from cooking too quickly when it contacts the hot crust.

5-Step 5: Prepare the Fruit Filling While the crust is baking and cooling, make your filling. In a large bowl, whisk together the 4 eggs and 2 cups of sugar until well combined and slightly thickened. Add the sour cream (or Greek yogurt), flour, and pinch of salt. Whisk until smooth and no flour lumps remain. Gently fold in the blackberries using a rubber spatula, being careful not to crush or break the berries too much. If using frozen berries, make sure they are completely thawed and drained of excess liquid before folding them in.

6-Step 6: Assemble and Bake Spoon the blackberry filling evenly over the partially baked crust, spreading it to all corners of the pan. Sprinkle the reserved 1 1/2 cups of crumb mixture evenly over the top of the filling. Don’t press down just let it sit naturally on the surface. Return the pan to the oven and bake for 45-55 minutes until the crust is lightly browned and the filling is set. You’ll know it’s done when the edges are bubbling and the center no longer jiggles like liquid when you gently shake the pan.

7-Step 7: Cool and Serve This is the hardest part waiting! Let the bars cool in the pan for at least 1 hour before attempting to cut them. For the cleanest cuts, refrigerate the cooled bars for an additional hour before slicing. Use a sharp knife to cut into 24 squares. Wipe the knife clean between cuts for the neatest presentation. Serve warm, at room temperature, or cold, depending on your preference. These bars pair wonderfully with a dollop of homemade whipped cream or a scoop of vanilla ice cream.