For crepes, in a blender container, combine milk, water, eggs, the 1/4 cup cooking oil, and the 1/2 teaspoon vanilla. Add flour and salt. Cover; blend until smooth. Transfer to a bowl. If you like, cover and refrigerate up to 4 hours.
Lightly oil a 6- or 7-inch skillet; heat over medium heat. Remove from heat. Stir batter. Ladle 2 to 3 tablespoons batter into skillet, lifting and tilting to spread batter. Return to heat; brown one side only. Invert over paper towels; remove crepe. Repeat with batter, adding oil as needed.
Layer half of the crepes (about 12) between pieces of foil or plastic wrap. Place in an airtight container; freeze for another use. Use remaining crepes immediately or layer with plastic wrap and store in refrigerator for several hours.
For filling, in blender container, combine cottage cheese, egg yolk, powdered sugar, the 1 teaspoon butter, and the lemon peel or vanilla. Cover and blend until smooth, scraping down side occasionally with a rubber spatula.
Spoon 2 tablespoons filling onto unbrowned side of crepe just below center. Fold bottom edge up and over filling. Fold opposite sides in until they meet. Roll up crepe from the bottom. Repeat for remaining crepes and filling.
In a large skillet, combine the 1 tablespoon cooking oil and the 1 tablespoon butter. Heat over medium heat until butter is melted. Place filled crepes, seam sides down, in skillet. Cook about 5 minutes or until blintzes are golden, turning once. Serve with sugar, sour cream, and preserves. Makes 12 blintzes.