Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper or a silicone baking mat.
In a small saucepan over medium heat, combine the blueberries, lemon juice, and sweetener (if using). Cook until the blueberries break down and form a thick consistency.
In a blender or food processor, blend the cottage cheese, egg yolks, vanilla extract, and sweetener until smooth.
In a clean mixing bowl, beat the egg whites and cream of tartar until stiff peaks form.
Gently fold one-third of the whipped egg whites into the cottage cheese mixture, then fold in the remaining egg whites.
Spoon mounds of the batter onto the prepared baking sheet, creating a slight well in the center of each mound. Spoon blueberry mixture into the wells and swirl gently.
Bake for 20–25 minutes, or until golden brown and set. Let cool for 5 minutes before transferring to a wire rack.
Serve warm or at room temperature.
