Green Bean Casserole With Crispy Fried Onions

Preparation

1. Casserole

   Step 1

   Preheat oven to 425º. Line 2 rimmed baking sheets with parchment paper. Arrange 2 lb. mixed wild mushrooms, trimmed, halved or quartered if large (about ½" pieces) and 2 thyme sprigs in a single layer on prepared baking sheets. Drizzle with ¼ cup extra-virgin olive oil and season with season with ¾ tsp. Diamond Crystal or ½ tsp. Morton kosher salt and ½ tsp. freshly ground black pepper. Roast mushrooms, stirring once and rotating pan halfway through, until lightly golden, crisp-tender, and liquid is evaporated (watch carefully as cook time can vary between types of mushrooms), 25–35 minutes. Remove sheets from oven and reduce oven temperature to 375ºF.

   Step 2

   Meanwhile, generously season a large pot of boiling water with salt. Blanch 2 lb. green beans (preferably haricots verts), trimmed, cut in half on the diagonal, in salted boiling water until crisp-tender, 3–5 minutes. Drain in a colander and rinse under cold water to stop cooking. Drain well, then layer on a rimmed baking sheet with paper towels and pat dry. Wipe pot dry.

   Step 3

   Melt 2 Tbsp. unsalted butter over medium-low heat in same pot. Add ⅓ cup finely chopped red onion and 2 large garlic cloves, very thinly sliced, and cook, stirring occasionally, until tender, 5–8 minutes. Stir in 2 Tbsp. all-purpose flour and cook, stirring occasionally, until aroma is mildly nutty, 4–6 minutes. Add 3 Tbsp. heavy cream and stir well to combine. Repeat twice, then stir in remaining cream, 1 cup low-sodium chicken broth or vegetable broth, 2 dried bay leaves, and remaining 2 thyme sprigs. Bring to a simmer and cook, stirring occasionally and scraping sides of pot, until sauce is the consistency of slightly thickened cream and coats the back of a wooden spoon, about 20 minutes (do not over-reduce). Discard thyme and bay leaves. Stir in 1½ tsp. finely grated lemon zest (from 1 medium lemon), ½ tsp. Diamond Crystal or ¼ tsp. + ⅛ tsp. Morton kosher salt, and ¼ tsp. freshly ground black pepper.

   Step 4

   Arrange beans and mushrooms in 3-qt. baking dish. Pour cream sauce over; stir to evenly coat. Bake casserole until sauce is thickened and bubbling around the edges, about 20 minutes.

   Do ahead: Green beans, mushrooms, and sauce can be cooked 3 days ahead; refrigerate in separate airtight containers. Let come to room temperature before using.

2. Fried onion topping and assembly

   Step 5

   Pour canola or vegetable oil into a large wide pot or high-sided skillet to a depth of ½". Place over medium-high heat until hot but not smoking (about 350° on a deep-fry thermometer). Line a rimmed baking sheet with paper towels.

   Step 6

   Whisk ½ cup fine-grind cornmeal, 2 Tbsp. cornstarch, 1½ tsp. paprika, 1 tsp. ground coriander, and 1 tsp. ground cumin in a large shallow bowl. Toss 1 medium red onion, thinly sliced into ⅛" rings crosswise with a mandoline or very sharp knife, separated into rings in cornstarch mixture to coat.

   Step 7

   Working in batches, fry onion rings, stirring and turning occasionally, until golden brown and crisp, 2–3 minutes. Using tongs or a slotted spoon, transfer to prepared sheet to drain. Season immediately with kosher salt and freshly ground black pepper.

   Step 8

   Top green bean mixture with fried onions and serve warm.

   Do ahead: Onions can be fried 1 day ahead. Let cool. Arrange in a flat layer on a paper-towel-lined rimmed baking sheet, cover loosely with foil, and store at room temperature. 
   
   Editor’s note: This green bean casserole recipe was first printed in October 2017 as ‘Green Bean and Mushroom Casserole.’ Head this way for Our Favorite Mashed Potatoes, a pecan-topped sweet potato casserole, and more essential Thanksgiving side dishes →