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Green Bean Casserole Recipe

Make Green Bean Casserole Recipe with creamy mushroom sauce and crispy fried onions for a crowd-pleasing side.

Ingredients

• 2 medium yellow onions (about 16 oz / 450 g total), peeled and very thinly sliced into rings
• 1 cup (240 ml) buttermilk, chilled
• 1 cup (140 g) all-purpose flour, divided (3/4 cup / 105 g for onions, 1/4 cup / 35 g for sauce)
• 1 3/4 teaspoons kosher salt, divided
• 1 teaspoon freshly ground black pepper, divided
• 2 cups (480 ml) neutral vegetable oil, for frying onions
• 2 lb (900 g) fresh green beans, trimmed and cut into 2-inch (5 cm) pieces
• 4 quarts (3.8 L) water, for blanching green beans
• 2 cups (480 ml) ice, plus additional cold water for an ice bath
• 4 tablespoons (56 g) unsalted butter
• 12 oz (340 g) cremini or white button mushrooms, cleaned and sliced
• 1 medium shallot (about 1.5 oz / 40 g), finely minced
• 3 cloves garlic, finely minced
• 1/4 teaspoon freshly grated nutmeg (optional)
• 1 cup (240 ml) low-sodium chicken broth or vegetable broth
• 1 1/2 cups (360 ml) whole milk, at room temperature
• 1/2 cup (120 ml) heavy cream, at room temperature
• 1 teaspoon Worcestershire sauce
• 1 teaspoon Dijon mustard
• 1/2 cup (50 g) finely grated Parmesan cheese
• 1/4 cup (15 g) panko breadcrumbs (optional, for extra topping crunch)
• 2 tablespoons (8 g) finely chopped fresh parsley, for garnish (optional)
• Cooking spray or 1 teaspoon neutral oil, for greasing the baking dish

Instructions

Step 1: Soak the Onions and Prep the Dredge

Toss the very thinly sliced yellow onion rings into a medium bowl and pour the chilled buttermilk over them so every ring is lightly saturated; let them rest for at least ten minutes while you whisk the dry dredge. In a shallow dish combine 3/4 cup all-purpose flour, 3/4 teaspoon kosher salt and 1/2 teaspoon freshly ground black pepper, fluffing them together so the flour is uniformly seasoned. This short soak softens the onion centers and helps the flour cling, giving you lacy, crisp edges after frying — think tapered, translucent rings with puffy centers ready for their golden transformation.

Step 2: Fry to Crisp, Drain and Cool

Lift small handfuls of the soaked onions, let excess buttermilk drip, dredge thoroughly in the seasoned flour and lower them into hot oil in batches; fry until light golden and crisp, about 3–5 minutes, then transfer to a paper towel–lined tray to drain and cool — keep them intentionally pale-golden since they will deepen in the oven. Once cooled, set aside about one-third for the final top and let the rest rest in a single layer so they keep their airy, crunchy texture.

Step 3: Blanch the Green Beans and Shock Them

Bring salted water to a rolling boil, add the trimmed 2-inch green beans and cook just until bright and tender-crisp, then plunge immediately into an ice bath to lock the vivid chartreuse color and firm snap. Drain thoroughly and pat dry so the beans sit glossy but not wet — they should look satin-sheen, with clean cut ends and uniform 2-inch lengths ready to accept the creamy sauce without becoming watery.

Step 4: Brown Mushrooms with Shallot and Garlic

Melt butter and cook the sliced creminis until they release their moisture and develop a warm, caramelized edge; add the minced shallot until translucent and finish with a quick sweep of garlic just until fragrant. The visual here is bronzed mushroom slices with crisped margins and tiny translucent shallot threads, glistening with butter — move them into the same matte ceramic bowl you’ll use for the sauce so the warm, glossy mushrooms and their fond live together and the utensil (a wooden spoon or small spatula) rests on the rim, carrying a smear of golden butter for continuity.

Step 5: Build the Creamy Mushroom Sauce and Combine with Beans

Sprinkle the remaining flour over the mushrooms to form a pale roux, then whisk in broth, whole milk and cream until the mixture becomes a smooth, gently simmering cream that thickly coats a spoon; finish with Worcestershire, Dijon, a hint of nutmeg and the grated Parmesan folded in until glossy. Fold the well-drained blanched green beans into this warm, velvety sauce until each bean is evenly coated — the result should be a creamy, clingy coating with visible mushroom ribbons and flecks of black pepper and parsley. Transfer this mixture into the prepared 9x13-inch rectangular baking dish, spread into an even layer and scatter two-thirds of the fried onions and optional panko over the top, leaving the reserved onions for a later, darker finish. Keep the rectangular baking dish visible on the surface, showing clean edges and the even, mound-free surface ready to bake.

Step 6: Bake, Finish with Reserved Onions, Rest and Serve

Bake until bubbling at the edges and lightly golden, then mid-bake scatter the reserved fried onions for a deeper golden crown and return briefly to finish; remove, let rest ten minutes so the sauce thickens and serving is neat, and if desired, finish with a scattering of finely chopped fresh parsley. Plate straight from the rectangular 9x13 dish so slices hold their shape and the top shows contrast between molten creamy sauce and crunchy, lacy onion morsels — serve hot within the first 30–45 minutes for best contrasting textures.

Notes

• Reserve one-third of the fried onions to add mid-bake for maximum crunch.
• Use an ice bath to stop the beans cooking instantly and preserve color.
• If sauce is too thin after baking, let the casserole rest 10 minutes to thicken before serving.