Step 1: For the Crumble Topping: In a medium bowl, combine 1 cup all-purpose flour, rolled oats, 1/2 cup granulated sugar, brown sugar, cinnamon, and a pinch of salt. Whisk until well combined.
Step 2: Add the cold, diced unsalted butter to the dry ingredients. Using your fingertips or a pastry blender, work the butter into the flour mixture until coarse crumbs form. Don’t overmix; you want some pea-sized pieces for texture. Place in the refrigerator to chill.
Step 3: For the Graham Cracker Crust: Preheat your oven to 350°F (175°C). Lightly grease a 9-inch springform pan.
Step 4: In a medium bowl, combine graham cracker crumbs, 1/4 cup granulated sugar, and melted unsalted butter. Mix until the crumbs are evenly moistened.
Step 5: Press the mixture firmly and evenly into the bottom of the prepared springform pan. Bake for 8-10 minutes until lightly golden. Remove from the oven and let cool slightly. Reduce oven temperature to 325°F (160°C).
Step 6: For the Lemon Blueberry Cheesecake Filling: In a large mixing bowl, using an electric mixer on medium speed, beat the room temperature cream cheese until smooth and creamy, about 2-3 minutes. Scrape down the sides of the bowl often.
Step 7: Gradually add 1 cup granulated sugar, beating until just combined and smooth. Do not overbeat.
Step 8: Beat in the sour cream, lemon zest, and vanilla extract until just incorporated.
Step 9: Add the eggs one at a time, beating on low speed until just combined after each addition. Be careful not to overmix.
Step 10: Gently fold in the fresh lemon juice.
Step 11: In a separate small bowl, toss the fresh blueberries with the remaining 1/2 cup all-purpose flour. This helps prevent them from sinking to the bottom.
Step 12: Gently fold the floured blueberries into the cheesecake batter until evenly distributed.
Step 13: Assembly and Baking: Pour the blueberry lemon cheesecake filling over the cooled graham cracker crust in the springform pan.
Step 14: Evenly sprinkle the chilled crumble topping over the cheesecake filling.
Step 15: Place the springform pan on a baking sheet. Bake for 60-75 minutes, or until the edges are set but the center still has a slight jiggle. The internal temperature should reach 150°F (65°C).
Step 16: Turn off the oven, crack the door open slightly, and leave the cheesecake inside for another hour to cool gradually.
Step 17: Remove from the oven and let it cool completely on a wire rack at room temperature.
Step 18: Once completely cool, cover loosely with plastic wrap and refrigerate for at least 4-6 hours, or preferably overnight, before serving. This chilling is crucial for the cheesecake to fully set and for flavors to meld.