Preheat your oven to 325°F (163°C). Grease a 9-inch springform pan and wrap the outside with aluminum foil to prevent water from seeping in during baking.

In a medium bowl, mix graham cracker crumbs, 1/4 cup sugar, and melted butter until combined. Press this mixture firmly into the bottom of the prepared pan. Bake for 8 minutes, then let cool.

In a small saucepan, combine blueberries, 2 tbsp sugar, and 1 tbsp water. Bring to a simmer over medium heat and cook for about 5 minutes until berries soften. Stir in cornstarch and cook for 1 more minute until thickened. Remove from heat and let cool.

In a large bowl, beat cream cheese and 1 cup sugar until smooth. Add eggs one at a time, beating after each addition. Mix in vanilla, flour, sour cream, lemon zest, and lemon juice until creamy.

Pour half of the cheesecake batter over the cooled crust. Spoon half of the blueberry mixture on top and use a knife to gently swirl it into the batter. Pour the remaining cheesecake batter over this layer, followed by the rest of the blueberry mixture. Swirl again to create a marbled effect.

Place the springform pan inside a larger baking dish and fill the outer dish with hot water until it reaches halfway up the sides of the springform pan. This water bath will help the cheesecake bake evenly.

Bake in the preheated oven for 60-70 minutes, or until the edges are set but the center still has a slight jiggle. Turn off the oven and let the cheesecake cool inside for 1 hour to prevent cracking.

Remove the cheesecake from the oven and let it cool completely at room temperature. Once cooled, refrigerate for at least 4 hours or overnight for the best flavor and texture.

Before serving, remove the cheesecake from the springform pan and slice into wedges. Enjoy!