01 - Whisk together flour and salt in a mixing bowl. Create a well in the center and add eggs and half the milk. Whisk until smooth, then gradually incorporate remaining milk and melted butter until batter reaches a slightly runny consistency. Allow batter to rest for 10 minutes.
02 - Heat a non-stick skillet over medium heat and brush lightly with melted butter. Pour approximately ¼ cup batter into skillet, swirling to coat surface thinly and evenly. Cook for 1–2 minutes until edges lift and bottom is golden. Flip and cook 1 additional minute. Transfer to a plate. Repeat with remaining batter.
03 - Heat olive oil in a skillet. Sauté onion until soft and translucent, then add mushrooms and cook until golden. Stir in spinach and cook just until wilted. Season generously with salt and pepper.
04 - Place 2 tablespoons filling and a sprinkle of cheese in center of each crepe. Fold or roll crepe around filling, then return to skillet to heat through and melt cheese, approximately 1–2 minutes per side.
05 - Serve immediately, garnished with fresh herbs if desired. Pair with a crisp white wine such as Sauvignon Blanc for a complete meal.