Prep the pan and oven: Heat oven to 325°F (163°C). Line the bottom of an 8- or 9-inch springform pan with parchment.
Lightly mist the sides with baking spray.
Make the crust: In a bowl, mix graham crumbs, sugar or sweetener, melted light butter, and a pinch of salt until the texture resembles damp sand. Press evenly into the pan, going slightly up the sides. Bake for 8 minutes, then set aside to cool slightly.
Beat the cream cheese: In a large bowl, beat reduced-fat cream cheese until smooth and fluffy, about 1 minute.
Scrape the bowl so no lumps remain.
Add yogurt and sweetener: Beat in Greek yogurt and sugar (or sweetener) until smooth. Avoid overbeating to keep air bubbles minimal.
Incorporate eggs: Add eggs one at a time, mixing on low until just combined. Do not whip.
Stir in vanilla, salt, and cornstarch.
Flavor it: Add key lime juice and zest. Mix on low until fully blended and creamy.
Pour and smooth: Pour filling over the crust. Tap the pan firmly on the counter 3–4 times to release air bubbles.
Smooth the top with a spatula.
Bake low and slow: Bake at 325°F (163°C) for 35–45 minutes, until edges are set and the center wobbles like Jell-O. If the top browns too fast, tent loosely with foil.
Cool gradually: Turn off the oven, crack the door, and let the cheesecake sit inside for 30 minutes. Move to a rack and cool to room temperature.
Chill to set: Cover and chill at least 4 hours, ideally overnight.
This step locks in the texture and brightens the lime flavor.
Garnish and serve: Top with a light dollop of whipped topping or a swipe of sweetened Greek yogurt. Add lime zest or slices. Slice with a hot, thin knife for clean edges.