Make the cheese filling by beating cottage cheese, pot cheese, 1 egg and sugar together. Combine the flour and milk with the 3 eggs. Beat to make a smooth batter.

Heat a 6- or 8-inch skillet. Coat with vegetable oil and pour in 2 to 3 tablespoons of the batter. Tilt the pan to distribute the batter over the bottom of the skillet. Cook until the dough is firm and browned.

Remove from the pan and place on a lightly-oiled plate with browned side up. Spoon 1 tablespoon of filling onto the edge of the pancake. Roll up by bringing the edge with the filling to the center of the pancake, fold in each side, and fold over once more to make a sealed pouch. Continue with the rest of the batter.

When ready to serve, heat the margarine in a skillet. Fry the blintzes until golden brown on all sides. Serve with yogurt.