Turkey Tetrazzini with a Crunchy Parmesan Panko Topping

INGREDIENTS

1 lb

spaghetti or linguine, cooked according to package directions

1/2 cup

unsalted butter, divided

1/2

sweet onion, chopped

garlic cloves, minced

1/4 cup

all-purpose flour

3 cups

low-sodium chicken stock or broth

2 cups

heavy cream

2 cups

shredded leftover turkey

1 cup

frozen peas

kosher salt & freshly ground black pepper

1 cup

panko breadcrumbs

1/2 cup

freshly grated parmesan