Step 1: Preheat oven to 350°F (175°C). In a medium bowl, combine graham cracker crumbs, 1/4 cup sugar, and 6 tablespoons melted butter. Press firmly into the bottom of a 9-inch springform pan. Bake for 8-10 minutes, then let cool.
Step 2: For the crumble topping, in a separate bowl, whisk together flour, 1/2 cup sugar, and cinnamon. Cut in the cold, cubed butter using a pastry blender or your fingertips until coarse crumbs form. Gently fold in 1 cup fresh blueberries and refrigerate.
Step 3: Reduce oven temperature to 325°F (160°C). Prepare a water bath by wrapping the outside of the springform pan tightly with heavy-duty foil. Place it in a larger roasting pan.
Step 4: In a large bowl, beat softened cream cheese on medium speed until smooth. Gradually beat in 1 1/2 cups sugar until well combined, scraping down the sides of the bowl.
Step 5: Add vanilla extract, lemon zest, and lemon juice; mix until just combined.
Step 6: Beat in eggs one at a time on low speed, mixing just until each egg is incorporated. Do not overmix.
Step 7: Pour the cheesecake filling over the cooled graham cracker crust. Evenly sprinkle the chilled lemon blueberry crumble topping over the filling.
Step 8: Carefully pour hot water into the roasting pan around the springform pan, reaching about halfway up its sides.
Step 9: Bake for 60-70 minutes, or until the edges are set and the center slightly jiggles. Turn off the oven, crack the door, and let the cheesecake cool in the water bath for 1 hour.
Step 10: Remove from water bath, unwrap foil, and cool completely on a wire rack at room temperature. Refrigerate for at least 6 hours, or preferably overnight, before serving.