Step 1: Prepare the Crust

1. Preheat the oven to 325°F (163°C).
2. Mix the graham cracker crumbs, sugar, and melted butter in a bowl until well combined.
3. Press the mixture firmly into the bottom of a 9-inch springform pan.
4. Bake for 8-10 minutes until lightly golden. Let it cool while preparing the filling.

Step 2: Make the Cheesecake Filling

1. In a large mixing bowl, beat the cream cheese and sugar until smooth and creamy.
2. Add the eggs one at a time, mixing on low speed to avoid overbeating.
3. Stir in the sour cream, vanilla extract, lemon juice, and cornstarch until just combined.
4. Pour the mixture over the cooled crust and smooth the top.

Step 3: Bake the Cheesecake

1. Water Bath Method (Bain-Marie): Wrap the bottom of the springform pan in aluminum foil and place it in a large roasting pan. Pour hot water into the roasting pan until it reaches about 1 inch up the sides of the springform pan.
2. Bake for 55-65 minutes, or until the center is slightly jiggly but the edges are set.
3. Turn off the oven and let the cheesecake cool inside for 1 hour with the door slightly open.
4. Transfer to the refrigerator and chill for at least 4 hours, preferably overnight.

Step 4: Prepare the Berry Glaze

1. In a small saucepan, combine the raspberries, blueberries, sugar, and lemon juice over medium heat. Stir until the berries break down.
2. Mix the cornstarch with water, then add it to the saucepan. Stir until the mixture thickens (about 3-4 minutes).
3. Strain through a sieve to remove seeds for a smooth glaze, or leave it as is for a more rustic texture.
4. Let the glaze cool before spreading it over the chilled cheesecake.

Step 5: Assemble and Serve

1. Pour the berry glaze over the top of the cheesecake, letting it drip over the sides.
2. Garnish with fresh raspberries, blueberries, and a dusting of powdered sugar for a stunning finish.
3. Slice, serve, and enjoy the ultimate cheesecake experience!