Combine eggs, whole milk, melted butter, flour, sugar, and salt. Blend in a standing blender or with an immersion blender until smooth. Add sparkling water and pulse a few times to combine.
Place a 10-inch nonstick skillet over medium heat (on my electric stove, I put the heat at 3.5 /10).
When the skillet is hot, rub or brush it with some butter. When the butter melts, pour 1/4 cup of batter into the pan, tipping the pan all around so that the batter stretches all the way to the edges. (Note: if the batter is not thin enough to easily spread out, add some more sparkling water to the batter in the blender until the batter reaches a very thin consistency.)
Let the crepe cook on one side until the edges are crisp and start to pull away from the pan and the bottom is golden brown, 2 to 3 minutes.
Flip the crepe and cook on the other side until golden brown. (If you’d like to add warm toppings, you can add some to the crepe as it cooks or wait and add them after cooking.)
Continue making crepes until all of the batter has been used. If you’d like to keep them warm until serving, you can line them up on a sheet pan, overlapping, in a warm (200 degree F) oven.
Fill or top crepes with your favorite fillings and serve immediately.