Prep the pan: Line the bottom of a 9-inch springform pan with parchment and lightly grease the sides.
Preheat oven to 300°F (150°C). Place a pan of hot water on the lower rack to create gentle humidity.
Make the crust (optional): Mix almond flour, melted butter, sweetener, and salt. Press firmly into the bottom of the pan.
Bake for 8–10 minutes until just set. Cool while you make the filling.
Beat the base: In a large bowl, beat softened cream cheese until smooth with no lumps, about 1–2 minutes on medium speed. Scrape down the bowl.
Add yogurt and sweetener: Mix in Greek yogurt and granulated sweetener until creamy.
Avoid whipping too much air into the batter.
Flavor it: Add cocoa powder, vanilla, buttermilk, vinegar, and salt. Mix until fully combined and smooth.
Blend in protein powder: Sift in the protein powder to prevent clumps. Mix on low until just incorporated.
If the batter is very thick, add 1–2 tablespoons milk.
Add eggs: Beat in eggs one at a time on low speed. Stop as soon as the streaks disappear.
Color: Stir in red food coloring until you reach a deep red velvet hue. Remember that baking slightly dulls the color.
Fill and smooth: Pour the batter into the prepared pan.
Tap the pan a few times on the counter to pop surface bubbles.
Bake low and slow: Bake at 300°F (150°C) for 35–45 minutes. The edges should be set and the center should still have a slight jiggle, like set Jell-O.
Cool gradually: Turn off the oven, crack the door, and let the cheesecake rest inside for 30 minutes. Then transfer to a rack and cool to room temperature.
Chill to set: Cover and chill at least 6 hours, preferably overnight.
This step ensures the best texture.
Finish and serve: If you like, spread a thin layer of sweetened Greek yogurt or add a light dollop of whipped topping. Slice with a warm, clean knife for neat edges.