In a medium bowl, whisk together the flour, sugar (if using), and salt until blended.

In another bowl, beat the eggs lightly, then add the milk and vanilla and whisk to combine.

Make a well in the center of the flour and slowly pour in the wet mixture while whisking continuously to avoid lumps. Keep whisking until the batter is silky and smooth.

Whisk in the melted butter until fully incorporated. The batter should be the consistency of heavy cream. If it seems too thick, add a splash of milk.

Cover and let the batter rest for at least 30 minutes at room temperature, or up to 48 hours in the refrigerator.

Heat a nonstick skillet or crepe pan over medium heat. Brush with a little melted butter.

Pour about 1/4 cup (60 ml) batter into the center of the pan, then immediately tilt and swirl the pan until the batter forms a thin, even circle.

Cook for 30-45 seconds until the edges lift and the underside is pale golden. Flip with a spatula and cook 10-20 seconds more.

Transfer to a plate and repeat, stacking finished crepes with a sheet of parchment between every few to keep them from sticking.

Add filling to the center of each crepe, fold or roll, and dust with powdered sugar or a squeeze of lemon.