Beat eggs in a bowl. Add milk, oil and 1/2 teaspoon salt. Beat in flour using an electric mixer until well blended. Let batter stand for 15 to 30 minutes.
Mix the remaining 1 teaspoon salt, cottage cheese, sugar, sour cream, egg yolk and cinnamon together in a bowl to make the filling.
Melt butter in a 15cm frying pan. Spoon a portion of the batter onto the pan; cook until lightly browned on the bottom, about 3 minutes. Turn out onto a tea towel. Repeat with the remaining batter, thinning with small amounts of water if necessary and greasing the pan after every 2 to 3 blintzes.
Preheat oven to 200 degrees C. Grease a baking tray.
Melt the remaining butter in the pan over low heat, about 1 minute.
Place a blintz on a clean work surface with the uncooked side up. Add 1 tablespoon filling and roll up, completely covering the filling. Place on the prepared baking sheet. Repeat with the remaining blintzes. Brush filled blintzes with melted butter.
Bake in the preheated oven until brown, 15 to 20 minutes.