Prepare the pan: Preheat the oven to 325°F (165°C). Line the bottom of a 6-inch springform pan with parchment paper and lightly grease the sides.
Make the optional crust: Mix the rolled oats, melted butter or coconut oil, maple syrup, and salt. Press the mixture firmly into the bottom of the prepared pan.
Blend the dairy: Add the cottage cheese and Greek yogurt to a blender or food processor. Blend until completely smooth and creamy with no visible cottage cheese curds.
Add the remaining ingredients: Add the eggs, vanilla protein powder, cornstarch, lemon juice, vanilla extract, sweetener, and salt. Blend just until the mixture is smooth and evenly combined.
Add the blueberries: Fold half of the blueberries into the cheesecake mixture. You can also pulse them briefly if you want more blueberry flavor throughout the filling.
Fill the pan: Pour the mixture into the prepared pan and gently smooth the top. Tap the pan lightly once or twice to remove large air bubbles.
Bake the cheesecake: Bake for 40–50 minutes, or until the edges are set while the center still has a gentle wobble.
Cool gradually: Turn off the oven and leave the cheesecake inside for about 10–15 minutes with the door slightly open. Remove and let it cool at room temperature.
Chill completely: Cover the cheesecake and refrigerate for at least 4–6 hours. For the firmest and creamiest texture, chill it overnight.
Add the topping: Top with the remaining fresh blueberries just before serving. Lemon zest or a spoonful of Greek yogurt can also be added.
Slice and serve: Run a warm, clean knife around the edge, cut into slices, and serve chilled.