Green Bean Casserole

Method

1. blanch5 min
   hard boil, heavily salted, then ice bath
   green beans + salt until they bend without snapping — about 4 minutes — then shock cold. The oven is only 20 minutes of moist heat and will not tenderize a raw bean; shocking also locks the color before the chlorophyll turns olive.
2. fry10 min
   350°F oil, in two batches
   onion tossed in dredging flour, shaken free of excess, fried until pale gold, then drained on paper and salted. They keep browning off the heat, so pull them early; a wet or thickly coated slice steams inside its crust and never gets brittle.
3. saute9 min
   medium-high, uncrowded
   butter + mushrooms, undisturbed until they weep, then until the pan is dry again and the edges brown. Mushrooms are ~90% water — if you stop while liquid remains, that water shows up later as a thin, gray sauce.
4. mix2 min
   medium
   + garlic + flour, stirring constantly for a full minute to cook the raw starch taste out of the roux before any liquid goes in.
5. reduce6 min
   low simmer
   + chicken stock whisked in gradually + heavy cream + black pepper + nutmeg (+ soy sauce), until it coats a spoon thickly — deliberately thicker than you want to eat, because the blanched beans will release water in the oven and thin it.
6. fold2 min
   off heat
   beans (patted dry) + mushroom cream into a shallow baking dish in a single even layer. Wet beans dilute the sauce; a deep pile steams rather than bakes.
7. bake20 min
   400°F, uncovered
   until the sauce bubbles at the edges and the surface has set enough to hold the topping.
8. top5 min
   400°F
   + fried onions (+ parmesan) for the last 5 minutes only. Added at the start they absorb steam from below and turn to soft paste — the contrast between crisp topping and creamy beans is the dish.