Ingredients:

  • 900 g (2 lbs) Fresh Green Beans (Haricots Verts, trimmed)
  • 3 L (100 fl oz) Water
  • 2 Tbsp (30 ml) Coarse Sea Salt (for boiling)
  • 1 large bowl Ice Water Bath
  • 4 large Shallots, thinly sliced into rings
  • 50 g (1/3 cup) All-Purpose Flour (for shallots)
  • 1/2 tsp Fine Sea Salt (for shallots)
  • 500 ml (2 cups) Neutral Oil (e.g., vegetable, rapeseed, or peanut oil)
  • 4 Tbsp (56 g) Unsalted Butter
  • 300 g (10 oz) Mixed Mushrooms (e.g., Cremini and Shiitake), thinly sliced
  • 2 cloves Garlic, minced
  • 4 Tbsp (50 g) All-Purpose Flour (for sauce roux)
  • 500 ml (2 cups) Whole Milk, warmed slightly
  • 250 ml (1 cup) Low-Sodium Chicken or Vegetable Stock
  • 120 ml (1/2 cup) Double Cream (Heavy Cream)
  • 1 tsp Dijon Mustard
  • 1/2 tsp Smoked Paprika
  • 1 tsp Fine Sea Salt (plus more to taste)
  • 1/2 tsp Freshly Ground Black Pepper
  • 60 g (1/2 cup) Freshly Grated Parmesan or Gruyère cheese (optional)

Instructions:

  1. Prepare the Green Beans: Bring a large pot of salted water to a rolling boil. Prepare the ice bath nearby. Add the trimmed green beans and cook for 3–5 minutes until vibrant green and tender-crisp. Immediately drain and plunge them into the ice bath to halt the cooking. Drain completely and set aside.
  2. Fry the Shallots: Heat the neutral oil in a deep skillet to 170°C (340°F). Toss the thinly sliced shallots with the 50g flour and 1/2 tsp salt until lightly coated. Working in batches, fry the shallots for 2–4 minutes until deeply golden brown and crispy. Remove the shallots with a slotted spoon to a paper towel-lined plate and lightly sprinkle with extra salt. Set aside.
  3. Sauté Mushrooms: Melt the butter in the same large skillet (wiped clean) over medium heat. Add the sliced mushrooms and sauté for 5–7 minutes until their liquid has evaporated and they are nicely browned. Add the minced garlic and cook for 1 minute more.
  4. Build the Roux: Sprinkle the 4 Tbsp of flour over the mushroom mixture. Stir continuously for 1–2 minutes until a thick paste forms, cooking out the raw flour taste. Slowly whisk in the warmed milk, a bit at a time, ensuring the mixture remains smooth. Then, whisk in the stock.
  5. Finish the Sauce: Bring the mixture to a gentle simmer, whisking occasionally, until the sauce thickens significantly. Stir in the heavy cream, Dijon mustard, smoked paprika, salt, pepper, and Parmesan/Gruyère (if using). Taste and adjust seasoning.
  6. Assemble and Initial Bake: Preheat the oven to 190°C (375°F). Lightly grease the baking dish. Gently fold the blanched green beans into the prepared mushroom sauce until evenly coated. Pour the mixture into the prepared baking dish. Bake for 20 minutes, or until the casserole is bubbly and the edges are set.
  7. Finish and Serve: Remove the casserole from the oven. Scatter the reserved crispy shallots evenly over the top. Return the dish to the oven for a final 5–10 minutes, just until the topping is hot but not burnt. Serve immediately.