1. Preheat oven to 350ºF (175ºC). Grease and line a 9-inch springform pan with parchment paper.
2. Mix crushed crackers with melted butter and press into the bottom of the pan. Bake for 10 minutes, then let cool completely.
3. Reduce oven temperature to 325ºF (160ºC).
4. In a large bowl, cream together cream cheese and 1 cup sugar until smooth. Add sour cream, cornstarch, and vanilla; mix until just combined.
5. Beat in eggs two at a time on low speed until just blended. Avoid overmixing.
6. In another bowl, toss blueberries with 1 tablespoon sugar, 1 tablespoon flour, and lemon juice.
7. Pour cheesecake filling over cooled crust. Evenly spread blueberry mixture on top.
8. For the crumble, combine 1/2 cup flour, brown sugar, melted butter, and cinnamon (if using) until coarse crumbs form.
9. Sprinkle crumble over the blueberries.
10. Place springform pan in a larger baking dish. Pour hot water into the larger dish until halfway up the sides of the springform pan (water bath).
11. Bake for 1 to 1 1/2 hours, until center slightly jiggles.
12. Turn off the oven and crack the door open to let the cheesecake cool inside for 1 hour.
13. Remove from water bath, then let cool to room temperature for another hour.
14. Refrigerate for at least 6 hours or overnight.
15. Optional: For glaze, whisk 1/2 cup powdered sugar with 2 tablespoons milk, 1/4 teaspoon vanilla extract, and a pinch of salt. Drizzle over the cheesecake before serving.