Combine the diced rhubarb, quartered strawberries, sugar, salt, water, and lemon juice in a saucepan over medium heat. Simmer for 6-8 minutes, stirring occasionally, until the fruit breaks down and releases its juices into a syrupy compote. The rhubarb will soften and lose its bright color while the strawberries become jammy. Transfer to a bowl and let cool to room temperature—this allows the flavors to meld and makes it easier to layer into the cheesecakes without melting the batter.

Preheat your oven to 325°F and line 18 muffin cups with paper liners. While the oven preheats, combine the graham cracker crumbs, sugar, and melted butter in a bowl until the mixture resembles wet sand. Press about 2 tablespoons of the crust mixture firmly into the bottom of each liner to create an even base. I like to use the bottom of a measuring cup to pack the crust down—it ensures they're all the same thickness so they bake evenly.

Using an electric mixer, beat the room-temperature cream cheese in a large bowl until completely smooth and creamy, about 2-3 minutes—this removes lumps and incorporates air for a lighter texture. Add the sugar, flour, and vanilla extract, mixing until just combined. Add the eggs one at a time, beating on low speed after each addition to avoid overmixing, which can incorporate too much air and cause cracks. Finally, gently fold in the sour cream by hand until just combined. I find that folding the sour cream in by hand at the end prevents overdeveloping the batter and keeps the cheesecake tender.

Divide the cheesecake batter from Step 3 evenly among the prepared liners, filling each about one-third full with roughly 2 tablespoons of batter. Top each with about 1 teaspoon of the cooled fruit compote from Step 1. Using a small knife or skewer, gently swirl the fruit into the batter with 2-3 small figure-eight motions—avoid over-stirring, which muddles the colors. Add another 2 tablespoons of batter to each liner, then top with another teaspoon of fruit compote. Swirl again with the same gentle technique. This layered swirling creates beautiful ribbons of fruit through the finished cheesecakes.

Place the muffin pans in the preheated 325°F oven and bake for 30-40 minutes. The cheesecakes are done when the edges are set but the centers still have a slight jiggle when you gently shake the pan—they should not be completely firm, as they continue to set while cooling. Remove from the oven and let cool in the pans for 15-20 minutes, then transfer to the refrigerator to chill completely, at least 2 hours. Chilling is essential; it firms up the filling and helps the flavors develop fully.