Green Bean Casserole from Scratch

Ingredients: 3 tablespoons canola oil, divided,1 medium onion, half diced and other half thinly sliced,8 ounces mushrooms, chopped,8 ounces mushrooms, chopped,1 tablespoon onion powder,1 1/4 teaspoons salt, divided,1/2 teaspoon thyme,1/2 teaspoon freshly ground pepper,2/3 cup all-purpose flour, divided,1 cup low-fat milk,3 tablespoons dry sherry (a fortified wine),1 pound fresh green beans (about 4 cups), cut in half,1/3 cup sour cream,1 teaspoon paprika,1/2 teaspoon garlic powder
Instructions:

1. Preheat oven to 400F. Coat a 2 1/2-quart baking dish with cooking spray.
2. Cook green beans in boiling salted water until crisp and tender.
3. Heat 1 tablespoon oil in a large saucepan over medium heat.
4. Add diced onion and cook until softened and translucent, about 4 minutes. Stir in mushrooms, onion powder, 1 teaspoon salt, thyme and pepper. Cook another 3 to 5 minutes.
5. Sprinkle 1/3 cup flour over the vegetables; stir to coat.
6. Add milk and sherry and bring to a simmer, stirring often to reduce flour lumps. Stir in green beans and return to a simmer. Cook, stirring, until heated through, about 1 minute. Stir in sour cream.
7. Transfer to the prepared baking dish.
8. Whisk the remaining 1/3 cup flour, paprika, garlic powder and the remaining 1/4 teaspoon salt in a shallow dish.
9. Add sliced onion; toss to coat.
10. Heat the remaining 2 tablespoons oil in a large nonstick skillet over medium-high heat.
11. Add the onion to oil and cook, turning once or twice, until golden and crispy, 4 to 5 minutes.
12. Spread the onion topping over the casserole.
13. Bake the casserole until bubbling, about 15 minutes.
14. Let cool for 5 minutes before serving.

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