Lunch: Mashed Potato and Cauliflower Gratin

Recipe by Gina Marie Miraglia Eriquez We love mashed potatoes in every way possible, but we're extremely partial to this incarnation paired with cauliflower. Since cheese is a natural with both potatoes and cauliflower, incorporating a little Fontina and

Ingredients

2 pounds russet (baking) potatoes, peeled and cut into 1-inch pieces
Salt
1 1/4 cups whole milk, divided
1 stick (8 tablespoons) unsalted butter, divided
4 ounces coarsely grated Italian Fontina or Gruyère (about 1 cup packed)
1/4 teaspoon freshly ground black pepper
1 (2- to 2 1/2-pound) head cauliflower, cut into 1 1/2-inch pieces, including stems and core
3 garlic cloves, peeled and smashed
3/4 to 1 cup grated Parmigiano-Reggiano, divided

Instructions

Put potatoes and 2 teaspoons salt in a large heavy saucepan and generously cover with cold water (about 2 1/2 quarts). Bring to a boil, then reduce heat, and simmer, partially covered, until potatoes are tender, 15 to 20 minutes.
While potatoes are boiling, heat 3/4 cup milk and 3 tablespoons butter in a small saucepan until butter is melted and milk is hot but not boiling. Keep warm off heat, covered.
Drain potatoes well in a sieve or colander and return to hot saucepan. Add milk mixture, Fontina, and pepper, and mash with a potato masher or fork to desired consistency. Season with salt and keep warm, covered.
Bring a pot of well-salted water to a boil, then add cauliflower and garlic and simmer until cauliflower is very tender, 13 to 15 minutes.
Drain cauliflower in a colander and pulse with remaining 1/2 cup milk, 1/2 cup Parmigiano-Reggiano, and 3 tablespoons butter in a food processor until it's a chunky purée.
Stir together mashed potatoes and cauliflower mixture in a large bowl and season with salt and pepper. Transfer to a buttered 3-quart flameproof shallow baking dish (not glass).
Heat oven to 425 °F with rack in middle. Melt remaining 2 tablespoons butter and gently brush over potato-cauliflower mixture, then sprinkle evenly with remaining 1/4 to 1/2 cup Parmigiano-Reggiano (to taste). Bake until potato mixture bubbles around edges, about 20 minutes.
Turn on broiler and broil 6 to 8 inches from heat until topping is browned in spots, 1 to 2 minutes.