French potato gratin

Ingredients:

• 1.3 kg. yellow potatoes, such as Yukon Gold, unpeeled, cut into 1/2-inch thick slices.
• 3 cups chilled milk (1% fat)
• 1/4 cup premium flour
• 2 cloves garlic, crushed
• 1 large or 2 small sprigs of thyme
• 1 and 3/4 cups grated Gruyere (170 g)
• 1.5 tsp salt

Preparation:

1. Preheat oven to 350°F (175°C) and spray a shallow 2-quart ovenproof dish with cooking spray.
2. Place the potatoes in a large saucepan and cover with water. Bring to a boil over medium heat. Reduce heat and simmer until the potatoes begin to soften, about 8 minutes. Drain and set aside to cool slightly.
3. Combine the milk and flour in a large saucepan and whisk until the flour dissolves. Add the garlic and thyme and cook over medium heat, stirring constantly, until the mixture comes to a boil and thickens, about 8 minutes. Remove from heat, discard the thyme sprig, and season with salt. Add 1 cup of cheese and stir until melted.
4. Place half the potatoes in a baking dish. Pour half the cheese sauce over them. Add the remaining potatoes and pour the remaining sauce over them. Sprinkle with the remaining cheese and bake for 25 minutes, until the sauce is bubbling. Place under the broiler and broil until the top of the casserole is golden brown, about 2 minutes. Serve hot.