Get Ready: Preheat your oven to 325°F (160°C). Line 18 muffin tins with paper liners – this makes for easy serving!
Make the Delicious Fruit Sauce: In a medium saucepan, combine the chopped rhubarb, strawberries, sugar, salt, and water. Cook this mixture over medium-high heat for about 6-8 minutes, stirring occasionally, until the rhubarb breaks down and the sauce is soft. Remove from heat and let it cool completely.
Prepare the Easy Crust: In a medium bowl, mix together the graham cracker crumbs, sugar, and melted butter until everything is well combined. Press about 2 tablespoons of this mixture firmly into the bottom of each paper-lined muffin cup.
Whip the Creamy Cheesecake: In a large bowl, beat the softened cream cheese until it's perfectly smooth and lump-free. Add the sugar, flour, and vanilla extract, then blend until the mixture is creamy and silky.
Add Eggs & Sour Cream: Gently mix in one egg at a time, just until it's combined – be careful not to overmix. Then, fold in the sour cream until it's smoothly incorporated into the cream cheese mixture.
Assemble Your Mini Treats: Spoon about 2 tablespoons of the cheesecake filling over the crust in each muffin tin. Dollop 1 teaspoon of the cooled strawberry rhubarb sauce on top. Use a butter knife to gently swirl the sauce into the cheesecake for a pretty marble effect.
Layer Up for More Swirls: Add another 2 tablespoons of cheesecake filling, then top with a generous teaspoon of strawberry rhubarb sauce. Swirl again with your butter knife, making sure the sauce is nicely distributed throughout each mini cheesecake.
Bake to Perfection: Bake at 325°F (160°C) for 30-40 minutes. Keep an eye on them; they're done when the centers are just set and no longer jiggle. (Dark muffin tins might cook a bit faster, so watch them closely!)
Chill & Enjoy: Remove the cheesecakes from the oven and let them cool completely. Then, transfer them to the refrigerator and chill thoroughly before serving. Store any leftovers in an airtight container.