01 -
Set the oven to 350°F (177°C) to prepare for baking.
02 -
Place cashews in a heatproof bowl and cover with just boiled water. Let soak while preparing the other components.
03 -
Bring a large pot of well salted water to a boil. Prepare an ice water bath. Add green beans to boiling water and cook for 3 minutes for thin beans, 4 minutes for regular beans, until tender-crisp. Drain and immediately transfer to the ice water to halt cooking. Once cooled, drain and set aside.
04 -
Heat avocado oil in a large skillet over medium heat. Add sliced shallots and cook, stirring often, until golden brown and crispy. Lower heat if necessary to prevent burning. Using a slotted spoon, transfer fried shallots to a plate lined with paper towel; season generously with salt. Reserve the oil in the skillet.
05 -
In the same skillet with the reserved oil, add diced onion and cook over medium heat until soft and translucent, about 3 minutes.
06 -
Add mushrooms to the skillet and cook until tender and caramelized, about 8 to 10 minutes. Stir in garlic, fresh thyme, Dijon mustard, salt, and black pepper, sautéing for about 1 minute.
07 -
Pour 1 cup of broth into the skillet, scraping up any browned bits. Lower heat and simmer for 5 to 6 minutes until the broth slightly reduces.
08 -
Drain soaked cashews. Blend cashews with 1/2 cup hot water in a high-speed blender until completely smooth and creamy.
09 -
Add the cashew cream, additional 1/2 cup broth, and nutritional yeast to the skillet. Bring to a simmer and cook, stirring often, for another 3 to 4 minutes until slightly thickened. Remove and discard thyme sprigs.
10 -
Add the blanched green beans to the skillet and toss with the sauce to coat. If all ingredients do not fit, transfer sauce and beans to the baking dish and mix well. Adjust seasoning with salt and pepper to taste.
11 -
Transfer coated green beans to a 9x13 inch baking dish. Bake uncovered for 20 minutes, until hot and bubbling.
12 -
Remove casserole from oven, scatter fried shallots over the top, and return to oven for an additional 5 minutes to crisp up the topping.
13 -
Serve casserole hot straight from the oven.