Roasted Garlic Mashed Potato and Mushroom Casserole

Instructions

1. Preheat oven to 400˚.
2. Cut off pointed end of garlic head and drizzle exposed cut cloves with olive oil.
3. Arrange garlic in on a double thickness of foil, cover with foil and seal edges tightly. Roast garlic on the middle rack of oven for about 40 minutes or until very soft. Cool, then squeeze garlic from skins. Reduce oven temperature to 350˚.
4. While garlic is roasting, bring large pot of salted water to a boil. Peel potatoes and cut into 1-inch chunks. Boil for 10 to 12 minutes or until tender. Drain.
5. Mash potatoes, roasted garlic, butter, sour cream and half-and-half or milk until smooth. Add more half-and-half or milk, if necessary, to make a creamy mixture. Stir in basil and season to taste with kosher salt and freshly ground pepper. Reserve.
6. Over medium-low heat, melt butter in a large sauté pan. Sauté leeks with a pinch of kosher salt for 5 minutes, stirring occasionally. Remove woody ends from mushrooms, wipe clean, slice and stir into leeks. Sauté an additional minute or until just beginning to sweat. (Do not overcook mushrooms or they will lose flavor; they will continue cooking in the casserole.)
7. In a 9X12-inch baking dish, evenly spoon 1/2 of mashed potatoes, spreading evenly with a spatula. Evenly layer leek and mushroom mixture over potatoes and top with remaining potatoes, smoothing with spatula. Sprinkle casserole with 1-2 cups grated cheese, according to taste.
8. Cover casserole with lightly greased foil and bake 30 minutes. Remove foil and bake an additional 15 minutes until cheese is lightly browned and bubbly.