01 - Whisk together flour and salt in a mixing bowl. Create a well in center, add eggs and half the milk. Whisk until smooth, gradually incorporating remaining milk and melted butter until slightly runny consistency. Rest batter for 10 minutes.
02 - Heat non-stick skillet over medium heat, brush lightly with melted butter. Pour ¼ cup batter, swirling skillet to coat thinly and evenly. Cook 1–2 minutes until edges lift and bottom is golden. Flip and cook 1 minute. Transfer to plate. Repeat with remaining batter.
03 - Heat olive oil in skillet. Sauté onion until softened. Add mushrooms, cook until golden. Stir in spinach, cook just until wilted. Season with salt and pepper.
04 - Place 2 tablespoons filling and cheese sprinkling in each crepe. Fold or roll. Return to skillet, heat through 1–2 minutes per side until cheese melts. Serve immediately, garnish with fresh herbs if desired.