Waste not, want not. You may be rolling your eyes and saying “Ok, Mom,” but we aren't handing out hoary old sayings just to amuse ourselves. In this meal, you'll be using the cauliflower in ways you've never used it before, and every part: the leaves, the core, and, of course, the florets. This versatile veggie is served with pasta and a rich, butter-y sauce that'll leave you licking the spoon… or the cauliflower. Nothing's wasted here, and everything tastes exactly as you want.
Remove leaves from cauliflower head and reserve. Core and cut into bite-sized florets. Cut core into thin slices. Halve and peel onion. Cut halves into ¼" slices. Halve garlic. Stem parsley. Coarsely chop leaves and mince stems, keeping them separate. Crush or coarsely chop pistachios.
Roast the Vegetables
Place cauliflower florets on a third of prepared baking sheet. Place cauliflower leaves on next third, and onion on final third. Add garlic, drizzle with 2 Tbsp. olive oil, and season with half the red pepper flakes (reserve remaining for garnish), ¾ tsp. salt, and a pinch of pepper. Roast until golden brown and tender, 20-25 minutes, rotating baking sheet halfway through. While vegetables roast, cook pasta.
Cook the Pasta and Cauliflower Core
Once water is boiling, add pasta and cook until al dente, 8-10 minutes. After 5 minutes, add cauliflower core slices to pot with pasta. Reserve 1¼ cup pasta water and drain in a colander. Drizzle with 1 tsp. olive oil, toss to coat, and set aside. While pasta cooks, start sauce.
Start the Sauce
Break butter into small chunks. Combine ¾ cup reserved pasta water, Parmesan, panko, butter, pistachios, parsley stems, and a pinch of pepper in a large mixing bowl.
Finish the Sauce
Tear cauliflower leaves and crush roasted garlic. Add pasta, cauliflower florets, onion, cauliflower leaves, crushed garlic, and parsley leaves (reserve a pinch for garnish) to bowl with sauce mixture. Combine thoroughly. If sauce is too thick, add remaining pasta water 1 Tbsp. at a time until desired consistency is reached.
Finish the Dish
Serve pasta and vegetables on a plate. Garnish with reserved parsley leaves and remaining red pepper flakes (to taste).