Not your average Green Bean Casserole!
1 carrot (peeled, cut into 2-inch pieces)
1 yellow onion (peeled, quartered)
1 fresh bay leaf
2 stalks celery (cut into 2-inch pieces)
2 pounds leftover white button mushroom stems and cremini stems
1 ounce mixed dried mushrooms
10 cups water
4 tablespoons unsalted butter
2 cloves garlic cloves (peeled, minced)
1 tablespoon thyme leaves (roughly chopped)
1/4 cup flour
2 cups mushroom stock
1/2 tablespoon sherry vinegar
1/4 cup heavy cream
2 teaspoons freshly grated nutmeg
Kosher salt and freshly ground pepper (to taste)
GREEN BEAN CASSEROLE:
2 pounds green beans (ends trimmed)
1/2 cup panko bread crumbs
1/4 cup Parmigiano Reggiano (freshly grated, plus more to garnish)
1/2 cup flour
1/2 cup cornstarch
4 shallots (very thinly sliced)
canola oil (for frying)
Kosher salt (to taste)
For the Mushroom Stock: Combine the carrot, onion, bay leaf, celery, mushroom stems, dried mushrooms and water and bring to a strong simmer.
Simmer until all of the flavor is released from the mushrooms and the stock reduces by about half, about 1 1/2 hours.
Strain and measure out 2 cups. Reserve the remaining stock for another use. The stock can be refrigerated up to 1 week or frozen and held for up to 6 months.
For the Mushroom Sauce: In a large braiser over medium-high heat, melt the butter over medium-high heat. Add the garlic and thyme leaves with a pinch of salt and cook until the garlic softens. Stir in the flour and cook until light and golden brown, about 1 minute.
Whisk in the mushroom stock then bring to a simmer. Cook, stirring occasionally until thickened and reduced slightly, about 40-45 minutes.
Stir in the sherry vinegar, heavy cream, nutmeg and set aside. Season with salt and pepper.
For the Green Bean Casserole: Preheat the oven to 400º.
Bring a heavily salted pot of water to a rolling boil. Drop the green beans in and cook for a few minutes, until tender with a slight crunch.
Remove from the pot and shock in ice water to stop the cooking.
Drain then slice the green beans on a bias. Stir sliced green beans into the thickened mushroom stock. Season with salt and pepper if necessary. Top with a thin even layer of panko bread crumbs and Parmigiano Reggiano.
Bake until golden brown and bubbly, about 20-30 minutes. Remove the green bean casserole from the oven, garnish with more Parmigiano Reggiano and fried shallots.
For the Fried Shallots: Heat a pot of oil to 370º. Combine the flour and the cornstarch and a pinch of salt in a bowl and add the sliced shallots. Separate the shallot rings to make sure they are all evenly coated.
Transfer to a strainer and shake off the excess flour mixture before adding to the hot oil. Cook until light golden brown and crisp, about 1 minute. Work in batches so as to not overcrowd the pan.
Remove the shallots using a metal strainer to a paper-towel lined plate. Season immediately with salt.
Tip: Save mushroom stems whenever cooking with mushrooms and store in a plastic bag. Freeze mushroom stems until you’ve accumulated enough to make a mushroom stock!