Whisk together in a large bowl, the buckwheat flour and salt. Add the egg and gradually whisk in the cold water until a smooth, fluid batter forms, similar in consistency to heavy cream. Cover and let the batter rest at room temperature for at least 30 minutes to fully hydrate the buckwheat.
1 cup Whole Buckwheat Flour, ½ teaspoon Salt, 1 large Egg, 1½ cup Cold Water
Cook the forestière filling
Heat a skillet over medium heat. Drizzle in the olive oil. Add the sliced onion and cook for 3–4 minutes, until softened and lightly golden. Add the mushrooms and cook 5–7 minutes, until they release their moisture and begin to brown. Stir in the spinach and cook just until wilted. Season lightly with salt and pepper, then remove from heat and set aside.
1 tablespoon Olive Oil, 6 pieces Button Mushroom, 2 cup Baby Spinach, ½ medium Yellow Onion
Cook the galettes
Heat a nonstick skillet or crêpe pan over medium heat and lightly grease it. Stir the batter, then ladle about ½ cup batter into the center of the pan. Quickly swirl to spread the batter into a thin circle. Cook for 1–2 minutes, until the edges begin to lift and the bottom is set.
While the first side of the crêpe is cooking, divide the white and yolk for the egg of this first crêpe.
4 large Eggs
Add filling and eggs
Flip the galette. Carefully pour the egg white onto the cooking crêpe. Use the back of the spatula to gently move the white around to spread it until it starts to cook. Gently place the yolk in the centre of the crêpe.
Spoon one-quarter of the mushroom–spinach mixture around the placed yolk. Sprinkle ¼ of the feta cheese, on top of the cooked veg. At this point, the egg white should be set but the yolk will remain soft. If the crêpe is cooking too fast, pull the pan from the heat for now.
½ cup Feta Cheese
Fold and Serve
Fold the four sides of the galette inward to form a square, leaving the egg yolk visible in the center. Continue cooking for another 30 seconds, just until warmed through.
Transfer to a plate and repeat 3 more times with the remaining batter and filling. Serve immediately while hot.