01 - Whisk together flour and salt in a mixing bowl. Create a well in the center, then add eggs and half the milk. Whisk until smooth before gradually incorporating remaining milk and melted butter. The batter should have a slightly runny consistency. Allow it to rest for 10 minutes.
02 - Heat a non-stick skillet over medium heat and lightly brush with melted butter. Pour approximately ¼ cup batter into the skillet, swirling quickly to coat the surface thinly and evenly. Cook for 1–2 minutes until edges begin to lift and the bottom turns golden. Flip carefully and cook for 1 additional minute. Transfer to a plate and repeat with remaining batter.
03 - Heat olive oil in a skillet over medium heat. Sauté the chopped onion until softened and translucent, approximately 3–4 minutes. Add sliced mushrooms and cook until golden brown, about 5 minutes. Stir in chopped spinach and cook just until wilted, about 2 minutes. Season generously with salt and pepper to taste.
04 - Place approximately 2 tablespoons of the vegetable filling in the center of each crepe, then sprinkle with grated cheese. Fold or roll the crepe around the filling. Return to the skillet seam-side down and cook for 1–2 minutes per side until heated through and cheese is melted.
05 - Arrange crepes on serving plates and serve immediately while hot. Garnish with fresh herbs such as parsley or chives if desired. Serve with a crisp white wine like Sauvignon Blanc for an authentic French experience.