Potato and Mushroom Gratin

Peel the potatoes and slice them very thinly, ideally using a mandoline for uniform thickness, which ensures even cooking. Place the sliced potatoes into a large mixing bowl.

To the sliced potatoes, add the large egg, 35g (2.5 tablespoons) of melted unsalted butter, and 120 ml (0.5 cup) of warm full-fat milk. Season generously with salt and freshly ground black pepper. Mix thoroughly with your hands to ensure every potato slice is coated, creating a creamy, binding base for the gratin.

In a large frying pan, melt 30g (2 tablespoons) of unsalted butter over medium heat. Add the finely diced large onion and the finely diced carrot. Sauté for 5-7 minutes until the vegetables soften and the onion becomes translucent. The caramelization of these aromatics will build a foundational layer of flavor for the gratin.

Add approximately 6-7 sliced mushrooms (half of your total mushrooms) to the pan with the sautéed onions and carrots. Cook until the mushrooms release their moisture and begin to brown, about 5-8 minutes. Stir in the minced garlic during the last minute of cooking to prevent it from burning.

Preheat your oven to 190°C (375°F). Lightly grease a baking dish (approximately 25x35 cm or 10x14 inches). Begin by spreading a layer of the seasoned potato mixture evenly across the bottom of the dish. Next, spread a layer of the sautéed onion, carrot, and mushroom mixture over the potatoes. Sprinkle with a portion of the grated mozzarella cheese and a small amount of the chopped fresh parsley and dill. Repeat these layers until all ingredients are used, ending with a layer of potatoes on top.

In a separate small saucepan, melt 20g (1.5 tablespoons) of unsalted butter over medium heat. Add the finely diced small onion and sauté until softened, about 3-4 minutes. Add the remaining 6-7 sliced mushrooms and cook until tender. Pour in 150 ml (0.6 cup) of heavy cream. Season with salt, freshly ground black pepper, 1 teaspoon of Italian herb mixture, and 0.5 teaspoon of dried garlic powder. Bring to a gentle simmer, then remove from heat.

Carefully pour the prepared cream sauce evenly over the assembled gratin. Ensure the sauce seeps into the layers. Sprinkle the top of the gratin generously with the remaining grated mozzarella cheese and the 4 tablespoons (60 ml) of breadcrumbs. This will create a beautiful, golden-brown crust.

Place the baking dish into the preheated oven. Bake for approximately 50 minutes, or until the potatoes are tender when pierced with a fork, the sauce is bubbly, and the top is golden brown and crispy. If the top browns too quickly, you can loosely cover it with aluminum foil.

Once baked, remove the gratin from the oven and let it rest for 10-15 minutes before serving. This allows the gratin to set, making it easier to serve and enhancing its texture. Garnish with a final sprinkle of fresh parsley and dill before enjoying this comforting dish with your loved ones. Cook with love!