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1
Preheat oven to 400F
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2
Coat a 2 1/2-quart baking dish with cooking spray.
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3
Heat 1 tablespoon oil & crushed pepper flakes in a large saucepan over medium heat; add diced onion and cook, stirring often, until softened and slightly translucent, about 4 minutes.
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4
Stir in mushrooms, onion powder, 1 teaspoon salt, thyme and pepper.
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5
Cook, stirring often, until the mushroom juices are almost evaporated, 3 to 5 minutes.
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6
Sprinkle 1/3 cup flour & roasted garlic over the vegetables; stir to coat.
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7
Add milk and sherry and bring to a simmer, stirring often.
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8
Stir in green beans and return to a simmer.
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9
Cook, stirring, until heated through, about 1 minute.
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10
Stir in sour cream and buttermilk powder.
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11
Transfer to the prepared baking dish.
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12
Whisk the remaining 1/3 cup flour, paprika, garlic powder and the remaining 1/4 teaspoon salt and pinch of crushed red pepper flakes (if using) in a shallow dish.
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13
Add sliced onion; toss to coat.
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14
Heat the remaining 2 tablespoons oil in a large nonstick skillet over medium-high heat.
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15
Add the onion along with any remaining flour mixture and cook, turning once or twice, until golden and crispy, 4 to 5 minutes.
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16
Spread the onion topping over the casserole.
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17
Bake the casserole until bubbling, about 15 minutes.
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18
Let cool for 5 minutes before serving.
