1 tablespoon butter, for frying the finished blintzes
Sour cream, for serving (optional)
For the crepes, in a medium bowl, whisk together the melted butter and eggs. Add the milk, then gradually add the flour, whisking until just blended. Let sit for one hour so the gluten can activate.
To make the filling, mix together the cottage cheese, egg yolks, sugar and vanilla until well combined. Set aside.
For the sauce, in a medium saucepan, combine the three cups previously frozen blueberries, sugar and cornstarch. Set over medium heat and stir until the sugar dissolves. Bring to a boil, stirring occasionally for two to three minutes, until the sauce thickens. Remove from the heat and add the fresh blueberries. Set aside.
Heat a 20 centimeter nonstick pan over medium heat. Using a pastry brush or paper towel, brush the pan with oil, then spoon about three tablespoons batter into the hot pan, swirling the pan quickly to thinly coat the surface. Fry on one side until cooked and the top is dry, about one to two minutes. Turn the crepe out onto a clean tea towel, making sure the browned side is turned upward. Re-oil the pan for each crepe. You should have 16–18 crepes in the end.
Once all the crepes are cooked, fill each one with a heaping tablespoon of the cheese mixture along one edge, browned side up. Fold in the sides and roll up like a burrito. Repeat until all the crepes are filled.
When you’re ready to serve, fry each blintz in butter until slightly crisp on both sides. Serve with blueberry sauce and sour cream.