The best potato casserole

Ingredients:

• 2 tbsp butter + extra for greasing the pan
• 4 medium potatoes with brown skin and white flesh (about 1 kg)
• 1.5 cups heavy cream (35%)
• 0.5 cup whole milk (4-6%)
• 2 cloves garlic, crushed
• 0.5 tsp fresh thyme leaves
• A pinch of freshly grated nutmeg
• 1 cup grated Gruyere (about 100 g) or any aged cheese
• 0.5 cup finely grated Parmesan (about 45 g)

Preparation:

1. Preheat oven to 350°F (175°C). Grease a 20cm square baking dish with unsalted butter.
2. Peel the potatoes and use a sharp knife or a mandoline to cut them into 0.3 cm thick slices.
3. In a medium saucepan, combine the diced potatoes, heavy cream, whole milk, 2 tablespoons butter, garlic, thyme, 1.5 teaspoons salt, 1/2 teaspoon black pepper, and nutmeg. Bring to a simmer over medium heat and cook, stirring occasionally, until the potatoes are tender but still hold their shape, about 5 minutes. Remove the saucepan from the heat.
4. Add the Gruyere and Parmesan, stirring gently to coat the potatoes completely. Pour the potato mixture into the prepared baking dish. Bake until golden brown on top and the potatoes are cooked through, about 45 minutes. Let rest for 10 minutes before serving.