Ingredients:
- 3 pounds russet potatoes, peeled and thinly sliced
- 2 cups heavy cream
- 1 cup whole milk
- 1 large onion, thinly sliced
- 2 tablespoons olive oil
- 3 cloves garlic, minced
- 1 packet (1 oz) French onion soup mix
- 1 ½ cups shredded Gruyère or Swiss cheese
- 1 cup shredded mozzarella or cheddar
- 1 teaspoon salt (adjust to taste)
- ½ teaspoon black pepper
- 1 teaspoon dried thyme (optional)
- 1 cup crispy fried onions (for topping)
Instructions:
1. Prepare the onions
- Heat the olive oil in a skillet over medium heat.
- Add the sliced onion and sauté for 10–12 minutes until caramelized and golden.
- Add the minced garlic for the last minute.
- Set aside.
2. Make the creamy sauce
- In a bowl, whisk together the heavy cream, whole milk, French onion soup mix, salt, pepper, and thyme.
3. Assemble the casserole
- Preheat oven to 375°F (190°C).
- Grease a 9×13 baking dish.
- Layer half of the sliced potatoes evenly in the dish.
- Spread half of the caramelized onions on top.
- Sprinkle with half the Gruyère and mozzarella.
- Pour half of the cream mixture over the layer.
- Repeat with remaining potatoes, onions, cheese, and cream mixture.
4. Bake
- Cover with foil and bake for 45 minutes.
- Remove foil, add crispy fried onions on top, and bake another 20–25 minutes, or until the potatoes are tender and the top is golden and crispy.
5. Rest & serve
- Let the casserole rest for 10 minutes before slicing to allow it to thicken.