Prep the pan. Line a mini muffin pan with 24 paper liners.
Lightly mist the liners with cooking spray to make peeling easier.
Heat the oven. Set it to 325°F (165°C). A moderate temperature helps the cups bake evenly and stay silky.
Make a quick crust. Crush the graham crackers into fine crumbs. You should get about 1/2 cup.
Divide a scant teaspoon of crumbs into each liner and press gently with the back of a spoon. You want a thin base, not a thick crust.
Soften the cream cheese. Make sure it’s truly soft. If needed, microwave in 10-second bursts until pliable but not warm.
This prevents lumps.
Mix the filling base. In a medium bowl, beat the cream cheese with the sugar (or sweetener) until smooth, about 1 minute. Scrape the bowl.
Add the yogurt and flavor. Whisk in the Greek yogurt, vanilla, lemon juice, zest (if using), and salt until silky.
Stabilize the batter. Sprinkle in the cornstarch and mix until fully incorporated. This keeps the cups creamy but set.
Finish with the egg. Add the egg and mix just until combined.
Don’t overbeat, or you’ll add air and risk cracks.
Fill the cups. Spoon the batter over the crumbs, nearly to the top. The cups won’t rise much.
Bake. Place the pan on the middle rack and bake for 12–15 minutes. The centers should look slightly jiggly, like set Jell-O.
They’ll firm up as they cool.
Cool gradually. Turn off the oven, crack the door, and let the cups rest for 5 minutes. Then transfer the pan to a rack and cool to room temperature.
Chill to set. Refrigerate at least 2 hours, uncovered for the first 30 minutes to prevent condensation, then covered. Top with a small berry or two before serving if you like.