Delicate French crepes with savory fillings

Ingredients

• 1 cup all-purpose flour
• 2 large eggs
• 1 1/4 cups whole milk
• 2 tablespoons unsalted butter, melted (plus extra for cooking)
• 1/4 teaspoon salt
• 1 cup grated Gruyère or Swiss cheese
• 4 slices cooked ham, chopped
• 1 cup sautéed mushrooms
• 1 cup fresh spinach leaves
• 2 tablespoons chopped fresh chives or parsley
• Freshly ground black pepper, to taste