Garlic Mashed Potato Gratin

Ingredients:

• 1 head of garlic + 2 cloves
• 2 teaspoons olive oil
• 4 sprigs of rosemary
• 165g unsalted butter, sliced, plus extra for greasing the pan
• 1.3 kg potatoes, peeled and cut into 5 cm pieces.
• 3/4 - 1 cup whole milk, warmed

Preparation:

1. Preheat oven to 375°F (190°C). Cut about 0.5 cm off the top of the garlic. Place the head cut side up on a piece of foil. Drizzle with olive oil and a pinch of salt. Cut a sprig of rosemary in half and place it on top of the garlic. Wrap in foil. Bake until the garlic is soft and golden, about 1 hour. Carefully unwrap the foil and let the garlic cool slightly, then squeeze the cloves out of the skins; discard the rosemary.
2. Meanwhile, grease a 2-quart (2-liter) baking dish with butter. Crush the remaining 2 cloves of garlic; add to a large saucepan along with the potatoes and the remaining 3 rosemary sprigs. Cover with 1 inch (2.5 cm) of cold water and season generously with salt. Bring to a boil, then reduce heat and simmer until the potatoes are tender, 15-18 minutes. Drain well and discard the rosemary sprigs.
3. Increase the oven temperature to 230°C. Puree the potatoes, baked and boiled garlic, and return them to the pan using a vegetable grinder. Alternatively, return the potatoes and boiled garlic to the pan along with the baked garlic and mash with a potato masher.
4. Add the butter and stir until melted. Gradually whisk in 3/4 cup of milk. If the puree still seems too thick, gradually whisk in the remaining 1/4 cup of milk. Season with salt to taste.
5. Transfer the mashed potatoes to the prepared baking dish. Bake until golden brown on top, 30-40 minutes.