Instructions

•(This step can be done 1 day in advance): Preheat the oven to 400 degrees. Slice the top off of a head of garlic. Place the rest of it on a sheet of aluminum foil, on a baking sheet. Drizzle the garlic head with olive oil and season with some salt and pepper. Crumple the foil around the garlic to seal. Place sheet with foil wrapped garlic in the oven and roast for 30 minutes. Remove from oven, let cool until you can comfortably handle it, then squeeze the garlic cloves into a bowl. Using a fork, mash the cloves into a paste.
•To make the crumb topping: Melt butter in a medium saucepan over medium heat. Add breadcrumbs and scallions/chives, stirring and cooking for a couple minutes until lightly toasted.
•Keep oven at 400 degrees, and grease a 9 x 13 casserole dish (you can also use a larger dish or ramekins, but you may need to adjust bake time).
•Cook pasta in a large pot of salted water according to instructions, until al dente. When finished, drain the pasta and keep 1/2 cup of the cooking water.
•In a large, heavy saucepan or sauce-pot, melt the 8 tbsp. butter over medium low heat. Whisk in flour and roasted garlic paste. Cook, stirring constantly, for 3 minutes until golden. Whisk in milk and bring to a boil, still stirring constantly, then reduce heat to a simmer and cook the sauce for 3 minutes. Then stir in the cheddar, Parmesan, and salt and pepper until creamy and combined.
•Stir cooked pasta and reserved pasta water into the sauce (it will be soupy). Pour mixture into prep’d casserole dish. Evenly coat the top with the crumb topping. Place the dish on a baking sheet (in case of bubbling over). Bake 20-25 minutes until golden brown and bubbly.