Preheat the oven to 300°F (150°C). Line a baking sheet with parchment paper.
Tilt the container of cottage cheese to pour off any extra liquid or use a fine-mesh strainer; blend until smooth.
Beat the egg whites with cream of tartar until stiff peaks form.
In another bowl, whisk together the egg yolks, blended cottage cheese, optional vanilla extract, lemon zest, sweetener, and cornstarch until smooth.
Gently fold the yolk mixture into the whipped egg whites using a spatula.
Fold in the fresh blueberries carefully and scoop onto the prepared baking sheet.
Bake for 25-30 minutes until golden brown and firm; allow to cool slightly before enjoying.