Sift the flour, sugar and salt into a bowl and set aside. Combine the egg, milk, butter and vanilla extract in another bowl and stir until smooth. Add this mixture to the dry ingredients and stir until blended into a relatively smooth batter. Let the batter rest for 30 minutes in the refrigerator. (The batter may be prepared to this point and stored in the refrigerator for up to 12 hours.).
Heat a crêpe pan or small skillet over medium heat. Brush the pan with melted butter. Pour a scant 1/4 cup batter into the crêpe pan, swirling and tilting the pan to coat the bottom. Cook (reducing the heat if necessary) until the first side is set and has a little color, about 2 minutes. Use a thin metal or heatproof rubber spatula to loosen the crêpe and turn it over. Cook on the other side until set and very lightly colored (the crêpe will not be as dark on the second side as on the first), 1 minute more. Stack the crêpes between layers of parchment or waxed paper as you cook.
Purée the cottage cheese and cream cheese in a blender until very smooth. Transfer to a bowl and stir in the sugar, egg and vanilla extract by hand. Keep refrigerated until you are ready to finish the crêpes.
Preheat the oven to 400 degrees F. Lightly brush a medium baking dish with melted butter.
Spoon or pipe about 2 tablespoons of the cheese filling onto each crêpe. Fold each crêpe into quarters, or fold the sides in to the center, then roll each crêpe up. Place the crêpes seam side down in the prepared baking dish. Drizzle with melted butter and bake until very hot, 8 to 10 minutes.
Serve immediately, 2 crêpes per serving, with fruit or compote.