Wash and dry all produce. Adjust rack to upper position and preheat oven to 425 degrees. Bring a large pot of salted water to a boil. Cut any large cauliflower florets into smaller pieces. Toss on a baking sheet with a large drizzle of olive oil, half the garlic powder, and 1/4 tsp chipotle powder (we’ll use more of the spices later).

Season cauliflower generously with salt. Roast in oven until tender, about 25 minutes, tossing halfway through. After done roasting, preheat broiler to high. Meanwhile, once water is boiling, add fusilli to pot. Cook until just barely al dente, about 8 minutes. Reserve 1/4 cup pasta cooking water, then drain.

Melt 1/2 TBSP butter in a medium pan over medium heat (use an ovenproof pan if you have one). Add panko and toast, stirring frequently, until golden brown, 3-4 minutes. Remove from pan and transfer to a plate or bowl.

Trim, then thinly slice scallions, keeping greens and whites separate. After draining fusilli, melt another 1 TBSP butter in pan used for panko over medium heat. Stir in scallion whites, flour, remaining garlic powder, and a pinch of chipotle powder. (TIP: Add another 1/4 tsp chipotle if you like it spicy.) Cook, stirring, until scallion whites are softened, about 1 minute.

Whisk milk and reserved pasta cooking water into pan with scallion whites. Bring to a simmer, then let bubble until starting to thicken, about 3 minutes. Remove pan from heat and add cream cheese and 3/4 cup cheddar (save the rest for the next step), stirring to melt. Season with salt. Stir in cauliflower and fusilli. TIP: If your pan isn’t ovenproof, transfer everything to a small baking dish at this point.

Mix panko with remaining cheddar, then scatter over mixture in pan. Place pan under broiler and broil until top is browned and cheese is melted, 2-3 minutes. (TIP: Keep an eye on this—you don’t want it to burn.) Carefully remove from broiler and sprinkle with scallion greens. Divide between plates and serve.