Tuna-Noodle Casserole with Cauliflower

INGREDIENTS

4 tbsp

unsalted butter, plus more for dish

8 oz

pappardelle or other similar wide noodles

Coarse salt and freshly ground pepper

1 lb

cauliflower, broken into 1-inch florets (about 4 cups)

medium yellow onion, finely chopped (about 1 1/4 cups)

stalks celery, cut at an angle into 1/8-inch slices (about 1 cup)

5 tbsp

all-purpose flour

2 cups

whole milk

2 cans

each) solid tuna in water, drained and flaked

1/2 tsp

hot sauce, such as Tabasco

1/4 cup

lightly packed fresh flat-leaf parsley leaves