Here's What You'll Need
cauliflower, butter, shallots, garlic, flour, milk, gruyere, parmigiano reggiano, rosemary, salt, pepper, nutmeg, olive oil, breadcrumbs, parsley
Place ¾" – 1" of water in a saucepan with a steamer basket. Bring to a boil. Place cauliflower in the basket, reduce heat, cover and cook for 5-7 minutes. Drain and set aside.
Melt butter over medium heat, then add 2 diced shallots. Cook 3 minutes, stirring occasionally. Add chopped garlic and cook 1 minute more.
Add flour, then cook for 1-2 minutes, stirring constantly. Slowly pour in hot whole milk, whisking entire time. Continue until there are no lumps of flour and the sauce is smooth.
Add Gruyere cheese, Parmesan, salt, pepper, and nutmeg. Whisk until the cheese has completely melted and the sauce is extremely smooth.
Place the steamed cauliflower into the prepared casserole dish, then pour the thickened sauce on top. Toss to thoroughly coat the florets with the cheese sauce.
In a small bowl, combine Gruyere, Parmigiano Reggiano, and breadcrumbs. Mix well, then sprinkle on top of the assembled gratin. Drizzle with olive oil.
Cook for 30 minutes, or until browned and bubbly on top. Sprinkle with chopped parsley, then serve immediately.