Ingredients

Steps

• Preheat your oven to 180°C.
• Fry sliced onions in oil until golden, then sauté mushrooms until softened and colored.
• Butter the bread slices and cut them into triangles.
• Layer half the bread in a greased dish, followed by half the onion-mushroom mixture and half the Gruyère.
• Repeat the layers with the remaining bread, vegetables, and Gruyère.
• Whisk eggs, milk, crème fraîche, and Parmesan together, then pour over the dish.
• Place the dish in a roasting tray filled two-thirds high with warm water.
• Bake for 35 minutes until the gratin is puffy and golden.