In a medium bowl, whisk together the flour and salt.
In a separate medium bowl, whisk the eggs. Add the milk and ½ cup water, whisk to combine.
Microwave the 2 tablespoons of butter on high power in 30 seconds intervals until just melted, stirring to dissolve any pieces. It should not be above 140ºF (60ºC) when added to the batter or the eggs will curdle.
Make a well in the flour mixture. Add the melted butter. Gradually add the liquid egg mixture. Constantly whisk until a smooth batter forms. Alternatively, in a blender, add the eggs, milk, ½ cup water, flour, salt, and melted butter. Blend on medium speed until smooth, about 40 to 45 seconds.
Strain the batter into a medium bowl to remove any clumps. Cover and refrigerate for 1 hour.
Once chilled, whisk in about ¼ cup of water to thin out the consistency. It should be similar to cream in texture.
Heat a 10-inch nonstick skillet over medium heat for 1 minute. Add ½ teaspoon butter, swirling to coat the pan. When melted, wipe the excess with a paper towel. There should be a thin film in the pan, coating the bottom and sides.
Add a ¼ cup (60ml) of the batter to the 6 o’clock position of the skillet. Moving quickly, lift the skillet, tilt it slightly to coat the pan, and then swirl several times in a circular motion to evenly cover the entire skillet. Fill in any holes with batter as needed.
Place the pan back over the heat. Cook until the edges pull away from the skillet and lightly golden brown underneath, about 45 seconds to 1 minute. Use a spatula to loosen. Use either your fingers or spatula to flip and cook until the bottom sets, about 10 to 30 seconds. Transfer the crepe to a plate.
Stack the crepes on top of each other to keep warm while making the next batch, loosely cover with foil.
Cook the remaining batter, wiping the pan clean and adding a thin layer of butter between each crepe.
Mushroom Filling
In a large skillet melt the butter over medium heat. Add the red onions and thyme, cook until fragrant, 1 minute. Add the minced garlic, saute for 30 seconds.
Add the sliced mushrooms, salt, and black pepper. Sauté until the mushrooms release all their water, about 5 to 6 minutes.
Add the baby spinach, stir and cook until wilted, 1 to 2 minutes.
Remove the pan from the heat, stir in the cream and parsley. Season with salt and pepper to taste.
Evenly fill each crepe with the mushroom mixture, about ⅓ cup, and sprinkle some gruyere cheese on top. Fold over each side to close. Garnish with parsley, serve immediately.
Notes
Recipe Yield: 8 crepes and 2 ½ cups of filling
Serving Size: 1 crepe and about ⅓ cup filling
Measuring the flour: If you don’t have a scale, use the dip and sweep method. Dip the measuring cup into the flour, then level the surface with the back of a knife.
Pan Size: For an 8-inch nonstick pan, grease with ¼ teaspoon butter, and 3 tablespoons batter (about 13 crepes). For a 12-inch nonstick pan, grease with ¾ teaspoon butter, and 5 tablespoons of batter (about 8 crepes).
Cooking Crepes: The crepes will steam but should not smoke. Take the pan off the burner and adjust the heat as needed. Do not overcook or they will be too crisp.
Making Batter in Advance: Store in an airtight container for up to 1 day. It may separate as it sits, so mix before using. Whisk in about ¼ cup of water to dilute.
Storing: Cool the crepes completely and stack on a plate, cover tightly with plastic wrap, then foil. Alternatively, place in a resealable plastic. Refrigerate for up to 3 days.
Freezing: Place a piece of parchment paper between each crepe. Cover tightly and place on a plate in the freezer or in a large resealable plastic bag for up to 1 month. Defrost in the refrigerator the day before using.
Reheating: In the microwave, place a damp paper towel over the plate of crepes and microwave for 30 seconds. In a skillet, reheat over medium-low until warmed through. In the oven, place on a sheet pan covered with aluminum foil and warm at 275°F (135°C) for about 10 minutes.
Making in Advance: Cool the vegetables, then store in an airtight container for up to 3 days. Reheat in a skillet over medium heat until hot, turn off the heat and stir in the cream.
For a Thicker Sauce: Whip the heavy cream, then gently fold in. Alternatively, stir in 2 to 4 tablespoons of sour cream, plain greek yogurt, or crème fraiche at the end of cooking with the heat turned off.