In a large bowl, whisk together the eggs, salt, and sugar.

Gradually whisk in the milk and flour until smooth. There may be a few small lumps, but that's okay.

Stir in the warm water and melted butter until combined.

Let the batter rest for at least 30 minutes at room temperature. This allows the gluten in the flour to relax, resulting in thinner and more pliable crepes.

Heat a lightly oiled skillet over medium heat.

Pour about 1/4 cup of batter into the pan, swirling the pan to coat the bottom with a thin layer of batter.

Cook for 1-2 minutes per side, or until golden brown and the edges begin to curl. A spatula will help loosen the edges if they stick.

Remove the crepe from the pan and stack on a plate. Repeat with the remaining batter, adding more oil to the pan as needed.

While the crepes are cooking, heat some vegetable oil in a separate pan over medium heat.

Add the chopped onion and cook until softened, about 5 minutes.

Add the sliced mushrooms and garlic, and cook until the mushrooms are softened and golden brown, about 10 minutes. Season with salt and pepper to taste.

In a saucepan, melt the butter over medium heat.

Whisk in the flour and cook for 1 minute, stirring constantly.

Slowly whisk in the milk, whisking constantly to avoid lumps.

Bring to a simmer and cook, stirring occasionally, until the sauce thickens, about 5-7 minutes.

Remove from heat and whisk in the nutmeg, salt, and shredded cheese until melted and smooth.

Spoon a generous amount of the mushroom filling onto the center of each crepe.

Fold the crepe into quarters or roll it up.

Place the filled crepes on a plate or serving dish.

Pour the warm cheese sauce over the crepes.

Serve immediately and enjoy!