Step 1: Preheat your oven to 350°F (175°C). Lightly grease a 9x13 inch baking dish.
Step 2: In a medium bowl, combine 1 ½ cups all-purpose flour, 1 cup rolled oats, ¾ cup granulated sugar, ½ teaspoon ground cinnamon, and ¼ teaspoon salt. Whisk until well combined.
Step 3: Add 1 cup (2 sticks) cold unsalted butter, cut into small cubes. Use your fingertips or a pastry blender to cut the butter into the dry ingredients until coarse crumbs form.
Step 4: Press about 2 cups of the crumble mixture evenly into the bottom of the prepared baking dish to form the crust. Reserve the remaining crumble mixture for the topping. Bake the crust for 10-12 minutes, or until lightly golden. Remove from oven and let cool slightly while you prepare the filling.
Step 5: In a large bowl, using an electric mixer, beat two 8-ounce blocks of full-fat cream cheese (softened) with 1 cup granulated sugar until smooth and creamy, about 2-3 minutes. Scrape down the sides of the bowl as needed.
Step 6: Beat in 2 large eggs one at a time, mixing well after each addition. Add 1 teaspoon vanilla extract, the zest of 1 large lemon, and 2 tablespoons fresh lemon juice. Continue to beat until just combined. Do not overmix after adding the eggs.
Step 7: Gently fold in 2 cups of fresh or frozen blueberries into the cream cheese mixture. If using frozen blueberries, lightly toss them with 1 teaspoon of flour before adding.
Step 8: Pour the blueberry lemon cheesecake filling over the cooled crust in the baking dish, spreading it evenly.
Step 9: Evenly sprinkle the reserved crumble topping over the cheesecake filling.
Step 10: Bake for 45-55 minutes, or until the filling is mostly set and the crumble topping is golden brown. A slight jiggle in the center is normal.
Step 11: Remove from oven and let cool completely on a wire rack. This is crucial for the cheesecake to set properly. Once cooled, cover and refrigerate for at least 4 hours, or preferably overnight, before serving. This chilling time allows the cheesecake to firm up, making it easier to slice and enhancing its flavor and texture. Pro tip: For easy storage and to preserve freshness, transfer any leftovers into airtight Basics Glass Food Storage containers.