In a high-speed blender, combine whole milk, water, large eggs, melted and cooled unsalted butter, fine sea salt, granulated sugar, and vanilla extract. Blend on high for about 30 seconds until the mixture is smooth and frothy.

Add the all-purpose flour to the blender last. Blend on high for another 20-30 seconds, stopping occasionally to scrape down the sides. The batter should be thin and pourable, resembling heavy cream.

Heat a non-stick skillet over medium heat for about 5 minutes. Brush a thin layer of melted butter into the skillet just before pouring the batter.

Pour 1/4 cup of the prepared batter into the center of the skillet, tilting the pan quickly in a circular motion to coat the bottom evenly. Cook for 1-2 minutes and flip.

Transfer the cooked crepe to a plate and repeat the process with the remaining batter, reapplying a small amount of butter to the skillet as needed.