Sherry vinegar balances the richness in the cream sauce for this Thanksgiving staple from Thomas Keller’s Bouchon Bistro in Yountville, California. A riff on the American classic, this recipe swaps the green beans for slender French-style haricots verts and the canned mushroom soup for a from-scratch mushroom cream sauce. The whole thing then gets a topping of crispy shallots before baking.
1. Cook haricots verts in an 8-qt. saucepan of boiling salted water until crisp-tender, 1–2 minutes. Drain and transfer to an ice bath until cold. Drain and pat dry using paper towels; transfer to a large bowl and set aside.
2. Add 3 tbsp. oil to pan; heat over medium-high. Cook mushrooms until browned, 8–10 minutes. Add cream, thyme, and garlic, and reduce heat to medium; cook, stirring occasionally, until cream is reduced by half, 8–10 minutes. Let cool slightly and discard thyme; transfer to a blender. Add vinegar, salt, and pepper; purée into a smooth sauce (consistency should be similar to thick pea soup; if necessary, add more cream). Transfer to bowl with haricots verts; toss to combine and spread into a 9″ x 13″ baking dish.
3. Heat oven to 400°. Wipe pan clean and add remaining oil; heat until a deep-fry thermometer reads 300°. Toss shallots in flour and, working in batches, fry until golden and crisp, 2–3 minutes. Using a slotted spoon, transfer shallots to paper towels to drain; season with salt and arrange over casserole. Bake until golden brown and bubbly, about 25 minutes.