1 cup cold water
1 cup cold milk
4 eggs
1/2 tsp salt
1 1/2 cups flour
4 tbsp melted butter
Julia Child's recipe, which offers these proportions to make two dozen or so crepes:
Julia places the liquids, egg and salt into a blender, and then adds the flour and then butter. I just whisk it together (in that order) by hand. You might be surprised at how thin the batter is, but that is correct -- to quote Julia, it should just "coat a wooden spoon." Cover and refrigerate for at least 2 hours.