Preheat your oven to 350°F (175°C). Lightly grease an 8x8-inch (20x20 cm) square baking dish. If making individual portions, grease muffin tins or ramekins.
In a blender or food processor, combine the cottage cheese, eggs, sweetener, vanilla extract, and cornstarch. Blend until completely smooth and creamy.
Gently stir in 1 cup of berries and the lemon zest, if using. Reserve the remaining ½ cup of berries for topping.
Pour the mixture into the prepared baking dish and spread evenly.
Bake for 35–40 minutes, or until set and lightly golden.
Let it cool for 10–15 minutes before slicing or serving. Top with the reserved berries and an extra sprinkle of sweetener.
