Ingredients
4 tablespoons unsalted butter, plus more for dish
8 ounces pappardelle or other similar wide noodles
Coarse salt and freshly ground pepper
1 pound cauliflower, broken into 1-inch florets (about 4 cups)
1 medium yellow onion, finely chopped (about 1 1/4 cups)
2 stalks celery, cut at an angle into 1/8-inch slices (about 1 cup)
5 tablespoons all-purpose flour
2 cups whole milk
2 cans (5 ounces each) solid tuna in water, drained and flaked
1/2 teaspoon hot sauce, such as Tabasco
1/4 cup lightly packed fresh flat-leaf parsley leaves
Preparation
Preheat oven to 375 degrees. Butter a 2 1/2-quart casserole dish. Cook pasta in a large pot of salted water 4 minutes. Add cauliflower; cook until tender, 4 to 5 minutes more. Reserve 1/2 cup water; drain pasta mixture. In same pot, melt butter over medium heat. Add onion and celery, season with salt, and cook until onion is softened, about 8 minutes. Add flour; cook, stirring, 2 minutes. Slowly stir in milk until mixture is thickened, about 3 minutes. Remove from heat; stir in pasta mixture, tuna, and hot sauce. Season with salt and pepper. If mixture is too thick, add reserved pasta water.
Transfer to prepared dish; cover with parchment-lined foil. Bake 15 minutes. Uncover, increase heat to 425 degrees, and bake until lightly browned, 10 to 12 minutes. Top with parsley; serve immediately.
