Preheat your oven to 325°F (163°C). Line a 12-cup muffin tin with cupcake liners.

1. In a small bowl, combine the graham cracker crumbs, sugar, and cinnamon (if using). Stir in the melted butter until the crumbs are well-coated.
2. Spoon about 1 tablespoon of the crust mixture into each muffin cup and press it down gently with the back of a spoon to form an even base.
3. Bake for 8-10 minutes, or until lightly golden. Remove from the oven and set aside to cool.
4. In a large mixing bowl, beat the softened cream cheese with the sugar until smooth and creamy.
5. Add the vanilla extract and eggs, one at a time, beating well after each addition.
6. Stir in the sour cream until fully combined.
7. Spoon the cheesecake filling over the cooled crusts, dividing it evenly between the 12 cups.
8. Bake for 18-20 minutes, or until the centers are set but slightly jiggly. The tops should be lightly golden.
9. Let the mini cheesecakes cool to room temperature, then refrigerate for at least 2 hours, or until fully chilled.
10. For the topping, combine the chopped rhubarb, strawberries, sugar, and lemon juice in a small saucepan. Cook over medium heat for 5-7 minutes, stirring occasionally, until the fruit is softened and the sugar has dissolved.
11. If you want a thicker topping, mix the cornstarch with water to form a slurry and stir it into the fruit mixture. Cook for another 1-2 minutes until the topping thickens.
12. Remove from heat and let the mixture cool to room temperature.
13. Once the mini cheesecakes have cooled and chilled, spoon the strawberry rhubarb topping generously over each one.
14. Serve immediately or store in the refrigerator until ready to serve.