Prep the pan and oven: Heat the oven to 325°F (163°C). Line the bottom of an 8- or 9-inch springform pan with parchment. Lightly mist the sides with nonstick spray.
Make the crust: In a bowl, combine crumbs, cocoa, sweetener, melted light butter, and salt.
Stir until it resembles damp sand. Press firmly into the bottom of the pan. Bake for 8 minutes, then set aside to cool slightly.
Soften the cream cheese: Ensure the cream cheese is truly at room temp.
This helps it blend smoothly and prevents lumps.
Mix the filling base: In a large bowl, beat the cream cheese with a hand mixer on low to medium until smooth, about 1 to 2 minutes. Add the sweetener and salt, and mix until combined.
Add yogurt and flavorings: Beat in the Greek yogurt, vanilla, and cocoa powder. Scrape the bowl as needed.
If using cornstarch, sift it in now and mix just until incorporated.
Add the eggs: Add eggs one at a time, mixing on low until just combined. Avoid overbeating to limit air bubbles.
Stir in chocolate: Gently mix in the melted, cooled dark chocolate until the batter is evenly colored and glossy.
Fill and smooth: Pour the batter over the crust. Tap the pan a few times on the counter to pop surface bubbles.
Smooth the top with a spatula.
Bake: Bake at 325°F for 35 to 45 minutes, depending on pan size. The edges should be set, and the center should still jiggle slightly like Jell-O. Do not overbake.
Cool gradually: Turn off the oven, crack the door, and let the cheesecake rest inside for 30 minutes.
Then move it to a rack and cool to room temperature.
Chill to set: Cover and refrigerate for at least 4 hours, preferably overnight. This step is key for texture and clean slices.
Slice and serve: Run a thin knife around the edge before unclipping the pan. Warm the knife under hot water and wipe dry between cuts for sharp, tidy slices.
Add berries or a light topping if you’d like.