Step 1 In the jar of a blender, blend the flour, eggs, milk, salt, sugar and 4 tablespoons butter with 1 1/4 cups water at high speed for 10 seconds, stop and scrape down the sides, then blend for 10 seconds more. Strain batter through a fine-mesh sieve. Cover and chill for at least 1 hour or overnight.
Step 2 Heat a crepe pan or nonstick saute pan over medium heat until a few drops of water sizzle when sprinkled on the pan. With a paper towel, spread a little butter on the pan, being sure to wipe most of it off.
Step 3Using a bowl or a measuring cup with a spout, pour enough batter to just cover the pan (for a crepe pan, a little less than one-fourth cup), immediately swirling the batter around until it covers the surface. If the batter seems too thick and doesn't spread quickly, add up to an additional one-fourth cup of water to the mixture and stir until blended. Adjust heat if necessary. If the batter sizzles when you pour it onto the pan, it's too hot; if it just lies there, it's too cold. The first one or two crepes are usually experiments.
Step 4When the edges of the crepe begin to turn golden and move away from the pan, after about 2 minutes, lift up the edge nearest to you using a spatula (an offset spatula works best). Flip the crepe over. Cook the second side of the crepe only long enough for it to set, less than a minute. Remove from the pan and start a stack of crepes, layering wax paper between each crepe as you cook more. Add more butter when needed with a paper towel.