Fresh Green Bean Casserole

This is a side dish, with eight portions per casserole. Fresh green beans need blanching before baking; canned beans have a different texture and are not a direct substitution here. Thorough draining and cooking the mushrooms until their liquid evaporates help prevent a watery sauce. For make-ahead preparation, blanch and drain the beans and make the sauce up to 1 day ahead, cool promptly in shallow containers and refrigerate separately at 40°F (4°C) or below. Keep all crispy onions dry and separate. At serving time, combine the chilled beans and sauce with half the onions, cover and bake at 375°F (190°C) until the center reaches 165°F (74°C), allowing roughly 35 to 45 minutes rather than the fresh assembly timing. Uncover, add the remaining onions and bake about 5 minutes to crisp them; this extra time is not included in the fresh recipe total. Contains milk and wheat; packaged onions and broth may contain soy or other allergens, so check labels. Vegetarian when the broth and onions are vegetarian. Nutrition is estimated per one-eighth batch, about 180 calories and 320mg sodium, using typical whole milk, butter and packaged fried onions; brands can change the estimate, especially sodium and fat. Accompaniments are excluded. Refrigerate leftovers in shallow containers within 2 hours and use within 3 to 4 days. Reheat to 165°F (74°C); the onion topping will soften during storage. This recipe has not been kitchen-tested; use the texture and temperature cues.