From Scratch Green Bean Casserole

For the casserole:

lbs. green beans, ends trimmed and cut in half

unsalted butter

button mushrooms, sliced

minced shallots

flour

half-and-half

chicken broth

low-sodium soy sauce

Kosher salt and freshly ground pepper

For the topping:

Canola oil, for frying

shallots, sliced thinly

Flour, for dredging