Onion Gratin

Ingredients

• 2 large onions, thinly sliced
• 2 tablespoons butter
• 1/4 cup all-purpose flour
• 2 cups milk
• 1 teaspoon salt
• 1/2 teaspoon freshly ground black pepper
• 1/2 cup grated Parmesan cheese
• 1/2 cup shredded Gruyere cheese

Directions

1. Heat the oven to 375 degrees F (190 degrees C). Butter or otherwise grease a 9-inch baking dish.
2. Combine the Gruyere cheese, Parmesan cheese, pepper and salt in a medium bowl, then put the bowl aside.
3. In a medium saucepan set over medium heat, whisk the milk with the flour until the mixture is smooth. Cook it while stirring constantly, until it turns thick and bubbly, then take it off the heat and set it aside.
4. Set a large skillet over medium heat and melt the butter. Add the onions and cook them until they are tender and lightly colored, about 10 minutes.
5. Spoon half of the onions into the prepared baking dish, then scatter half of the cheese mixture over them. Add half of the milk mixture on top, then repeat the same layers with what remains.
6. Bake in the hot oven for 30 minutes, until the top is golden brown and the edges are bubbling. Let the gratin rest for 5 minutes before serving.