Tuna Noodle Casserole with Potato Chip Topping

INGREDIENTS

Kosher salt and freshly ground black pepper

4 tbsp

unsalted butter, plus more for the baking dish

medium onion, finely chopped

8 oz

cremini mushrooms, sliced

1/4 cup

all-purpose flour

2 cups

whole milk

1 cup

chicken broth

8 oz

medium pasta shells (about 3 cups)

jar Italian tuna in olive oil, drained and flaked

2 tbsp

chopped fresh flat-leaf parsley

2 cups

grated sharp white Cheddar

1 1/2 cups

crumbled flavored potato chips, such as salt-and-vinegar, onion or jalapeno