Step 1: In a large bowl, whisk together the flour, sugar (if using), and salt until combined.
Step 2: In a separate medium bowl, lightly whisk the eggs. Add the milk, water, and melted butter to the eggs and whisk until well combined.
Step 3: Gradually add the wet ingredients to the dry ingredients, whisking continuously until a smooth batter forms. Be careful not to overmix, as this can develop the gluten too much, leading to tough crepes. A few small lumps are okay, as they will disappear during resting.
Step 4: Cover the bowl with plastic wrap and refrigerate the batter for at least 30 minutes, or up to 2 hours. This resting period allows the flour to fully hydrate and the gluten to relax, resulting in more tender crepes that are less likely to tear.
Step 5: Heat a 6-8 inch non-stick crepe pan or skillet over medium heat. Lightly butter the pan (you may only need to do this for the first few crepes if your pan is well-seasoned).
Step 6: Pour 1/4 cup of batter into the center of the hot pan. Immediately tilt and swirl the pan to evenly coat the bottom with a thin layer of batter. Work quickly to ensure an even coating.
Step 7: Cook for 1-2 minutes, or until the edges start to crisp and turn golden brown and the surface looks set. Gently lift an edge with a spatula to check the color.
Step 8: Carefully flip the crepe and cook for another 30-60 seconds on the second side, until lightly golden. Transfer the cooked crepe to a plate.
Step 9: Repeat with the remaining batter, stacking the cooked crepes on top of each other. Keep them warm by covering the stack with foil or placing the plate over a pot of simmering water. Serve immediately with your favorite sweet or savory fillings.