Tuna Noodle Casserole With Asparagus

INGREDIENTS

1 stick

unsalted butter, plus more for the baking dish

12 oz

wide egg noodles

1 lb

(1 bunch) asparagus, trimmed and cut into 1-inch pieces

1 cup

frozen peas

1 cup

panko bread crumbs

kosher salt and black pepper

1/2

small onion, finely chopped

1/3 cup

all-purpose flour

5 cups

whole milk

8 oz

Cheddar, grated (about 2 cups)

2 5 ounce cans

tuna, drained

1 tbsp

chopped fresh tarragon or 1 teaspoon dried tarragon