Preheat your oven to 325°F (160°C) and line a muffin tin with paper liners.
In a mixing bowl, combine graham cracker crumbs, sugar, and melted butter. Mix until the crumbs are well-coated and resemble wet sand.
Press about a tablespoon of the crumb mixture into the bottom of each muffin cup, flattening with the back of a spoon. Bake for 10 minutes and then remove to cool.
In a medium bowl, beat the softened cream cheese until smooth. Gradually add 1 cup of sugar and vanilla extract, mixing well.
Add eggs one at a time, beating on low speed until combined (do not overmix to avoid cracks).
In a small saucepan, heat the mixed berries and lemon juice over medium heat. Stir gently until the berries start to break down (about 5 minutes). Add cornstarch and stir until thickened. Remove from heat and let cool slightly.
Pour the cream cheese mixture over the cooled crust in the muffin tin, filling each cup about 2/3 full.
Drop spoonfuls of the berry mixture on top of the cream cheese mixture and use a toothpick to swirl gently for a marbled effect.
Bake for 18-20 minutes or until the centers are set but still slightly jiggly.
Once baked, let the cheesecakes cool at room temperature before refrigerating for at least 4 hours (or overnight).
Notes
Serve chilled with a dollop of whipped cream and fresh berries on top for a vibrant and inviting finish.