Step 1 Place the water, milk, eggs and salt in a blender. Add the flour, then the butter. Cover and blend at top speed for 1 minute. If bits of flour adhere to the sides of the blender jar, dislodge them with a rubber scraper and blend for 2 to 3 seconds more. Cover and refrigerate the batter for at least 2 hours.
Step 2 Brush a skillet lightly with the oil (or rub it with the bacon fat). Heat it over medium-high heat until the pan is just beginning to smoke.
Step 3Immediately remove the pan from the heat, and, holding the handle of the pan in your right hand, pour with your left hand a scant 1/4 cup of batter into the middle of the pan. Quickly tilt the pan in all directions to run the batter all over the bottom of the pan in a thin film. (Pour any batter that does not adhere to the pan back into your bowl; judge the amount for your next crepe accordingly.) This whole operation takes 2 or 3 seconds. The batter should be a very light cream, just thick enough to coat a wooden spoon. If, after making your first crepe, it seems too heavy, beat in a bit of water, a spoonful at a time. Your cooked crepe should be about 1/16 inch thick.
Step 4Return the pan to heat for 60 to 80 seconds. Then jerk and toss the pan sharply back and forth and up and down to loosen the crepe. Lift its edges with a spatula, and if the underside is a nice light brown, the crepe is ready for turning.
Step 5Turn the crepe by using two spatulas; or grasp the edges nearest you in your fingers and sweep it up toward you and over again into the pan in a reverse circle; or toss it over by a flip of the pan.
Step 6Brown lightly for about 30 seconds on the other side. This second side is rarely more than a spotty brown, and is always kept as the underneath or nonpublic aspect of the crepe.
Step 7Slide the crepe onto the plate. Grease the skillet again, heat to just smoking and proceed with the rest of the crepes. As soon as you're used to the procedure, you can keep two pans going at once and make 24 crepes in less than half an hour.
Step 8Crepes may be kept warm by covering them with a dish and setting them over simmering water or in a 200-degree oven. Or they may be made several hours in advance and reheated when needed.