In a high-speed blender, combine the flour, milk, water, melted butter, granulated sugar, and kosher salt. If you're making sweet crepes, toss in the vanilla extract as well. Blend the mixture until smooth, about 30 seconds. You want it to be thoroughly combined, and it should have some air bubbles forming on the surface. This means you're on the right track!

Once the batter is blended, let it sit at room temperature for at least 30 minutes. If you want to take your time, placing it in the refrigerator overnight works wonders too. This aging process allows the gluten to relax, leading to tender crepes. When you're ready to use it, just give it a good whisk to reintroduce any elements that may have settled.

Place a nonstick skillet over medium heat. Let it warm up for a few minutes. You want it hot enough that a drop of water dances on the surface; this indicates it's ready to cook crepes. For an added layer of flavor, lightly spray the skillet with nonstick cooking spray or a pat of butter.

Using a measuring cup, pour 1/4 cup of batter into the center of the skillet. Immediately tilt the pan in a circular motion to spread the batter out evenly and completely cover the bottom. If you're using a bigger skillet, just increase the batter accordingly to ensure it fills the base.

Let the crepe cook for around 2 minutes or until the edges start to lift and the underside turns a lovely shade of golden brown. Keep a close eye on it - crepes cook fast! When it's ready to flip, use a spatula to carefully lift the edges and gently turn the crepe over. Let it cook for an additional minute or so on that side.

Once both sides are cooked, slide your crepe onto a plate and repeat the process until you’ve used up all the batter. Stack them on a plate and keep them warm, covered with a clean kitchen towel. They should remain soft and pliable, ready for all those delicious fillings!