Combine in a blender or food processor until smooth:
      1/2 cup all-purpose flour
      1/2 cup milk
      1/4 cup lukewarm water
      2 large eggs
      2 tablespoons unsalted butter, melted
      1/2 teaspoon salt
Pour the batter into a pitcher or other container with a pouring lip. Cover with plastic wrap and let stand for 30 minutes or refrigerate for up to 2 days. (This allows the flour to thoroughly absorb the liquid and gives the gluten in the flour a chance to relax.)
Place a nonstick or seasoned crêpe pan over medium heat. Coat the pan with a little:
      Unsalted butter
Stir the batter and pour about 2 tablespoons into the pan, lifting the pan off the heat and tilting and rotating it so that the batter forms an even, very thin layer. Cook until the top is set and the underside is golden. Turn the crêpe over, using a spatula or your fingers (fingers work best here) and cook until the second side is lightly browned. Remove the crêpe to a piece of wax paper. Continue cooking the rest of the crêpes, buttering the pan and stirring the batter before starting each one. Stack the finished crêpes between sheets of wax paper. Use immediately or let cool, wrap airtight, and  freeze for up to 1 month.