Before starting, preheat oven to 425°F. Wash and dry all produce.Heat Guide for Step 6 (dbl for 4 ppl): 1/4 tsp mild, 1/2 tsp medium and 1 tsp spicy! Add 10 cups water and 2 tsp salt to a large pot. (NOTE: Use same for 4 ppl.) Cover and bring to a boil over high heat. While the water comes to a boil, cut cauliflower into bite-sized pieces. Thinly slice chives.

Toss cauliflower with 1 tbsp oil (dbl for 4 ppl) on a baking sheet. Season with half the garlic salt and pepper. Roast in the middle of the oven, until golden-brown, 14-16 min.

While cauliflower cooks, add rigatoni to the pot of boiling water. Cook, uncovered, stirring occasionally, until tender, 10-12 min. Reserve 1/3 cup pasta water (dbl for 4 ppl), then drain and return to same pot, off heat.

Heat a large non-stick pan over medium heat. When hot, add 1 tbsp butter (dbl for 4 ppl), then onions. Cook, stirring often, until softened, 3-4 min. Sprinkle over flour and remaining garlic salt. Cook, stirring often, until onions are coated, 1 min. Add 1/2 cup milk (dbl for 4 ppl), then bring to a boil. Cook, stirring often, until thickened, 1 min. Remove the pan from the heat, then add spinach. Stir, until wilted, 1 min.

Stir sour cream and cheddar cheese into sauce. Season with salt and pepper. Add cheese sauce, reserved pasta water and half the cauliflower to the pot with the rigatoni. Stir until cheese melts, 1 min.

Divide pasta between bowls and top with remaining cauliflower. Sprinkle chives and 1/4 tsp chili flakes over top. (NOTE: Reference heat guide.)