In a blender (or in a bowl with a whisk), combine the milk, water, eggs, 2 Tbsp. melted butter (1/2 the butter), 1/4 tsp. salt and the flour and blend it until fully combined (but don’t over mix.) Set the batter aside.
Heat a medium to large heavy skillet over medium heat, and when it is hot, add 2 tsp. of butter. When the butter is bubbling, add the mushrooms and remaining salt and stir to coat. Saute them for 5 minutes until the release their juices.
Add the garlic and stir it in for 30 seconds until it is fragrant.
Add the spinach, let it wilt for a minute or two, and then stir in the goat cheese and continue cooking for 1 more minutes until the goat cheese is evenly spread through the mixture. Turn the skillet to the lowest heat.
In a crepe pan or small to medium (8 – 10-inch) nonstick skillet, heat 1/2 tsp. of butter and when it is bubbling, add 1/4 cup of the batter and tilt the pan to spread it out thinly. Let it cook for 1 – 1 1/2 minutes until the edges are fully cooked.
Put about 1/4 cup of spinach-mushroom filling down the middle of the crepe, and fold the sides of the crepe over the filling to make a log shape.
Set it aside on a serving platter and cook the rest of the crepes, adding 1/2 tsp. of butter after every other crepe if needed. Serve immediately.