1To make the crêpe better, combine the milk, egg, butter or oil, flour, sugar (if you're using it) and salt in a blender and pulse until smooth, scraping down the sides once or twice. Let the batter sit for 20-30 minutes - it should have the consistency of heavy cream.
2To make the crêpes, set a smallish skillet (well-seasoned cast iron is ideal, and maintains an even heat) over medium-high heat and drizzle with oil or spray with nonstick spray. Consider the first a practice; pour a few tablespoons' worth of batter into the pan and quickly swirl it to coat the bottom - cook until the edge starts to curl from the pan and it's golden on the bottom. Slide a thin spatula under the edge and flip; cook for another minute, until golden on the other side. Repeat with the remaining batter. (Crêpes can be made ahead, covered and refrigerated for up to a day.) Makes about 1 dozen crêpes.