Nutrition per serving may change if servings are adjusted.
Canola oil cooking spray
1 large onion, divided
1 cup buttermilk
¼ cup gluten-free all-purpose flour
1 teaspoon ground pepper, divided
2 pounds green beans, trimmed and cut into 1-inch pieces
1 tablespoon extra-virgin olive oil
1 pound mushrooms, chopped
2 cloves garlic, minced
1½ teaspoons salt
¾ teaspoon dried thyme
1½ cups low-fat milk
¼ cup water
2 tablespoons cornstarch
Preheat oven to 400°F. Coat a rimmed baking sheet with cooking spray. Coat a 9-by-13-inch baking dish with cooking spray.
Cut onion in half; thinly slice one half and dice the other half. Combine the sliced onion in a small bowl with buttermilk; let stand for 10 minutes. (Set the diced onion aside.)
Drain the sliced onion (discard the buttermilk). Add gluten-free flour and ¼ teaspoon pepper to the onion and toss to coat. Spread out on the prepared baking sheet and coat with cooking spray. Bake for 10 minutes. Stir and continue baking until the onion slices are golden brown, about 10 minutes more.
Meanwhile, bring 1 inch of water to a boil in a large pot fitted with a steamer basket. Add beans, cover and steam until tender-crisp, 3 to 4 minutes. Remove the beans and basket from the pot.
Wipe the pot dry. Add oil and heat over medium heat. Add the diced onion and cook, stirring often, until softened, about 4 minutes. Stir in mushrooms, garlic, salt, thyme and the remaining ¾ teaspoon pepper; cook, stirring often, until the mushrooms are tender and the mushroom liquid is almost evaporated, 3 to 5 minutes.
Pour in milk and bring to a simmer. Combine water and cornstarch in a small bowl. When the milk is simmering, stir in the cornstarch mixture and cook, stirring, until thick enough to coat the back of a spoon, 1 to 2 minutes. Stir in the green beans. Transfer the mixture to the prepared baking dish. Top with the crispy onion slices.
Bake the casserole until bubbling, 20 to 30 minutes.
82 calories;2 g fat(1 g sat); 3 g fiber; 13 g carbohydrates; 4 g protein; 39 mcg folate; 2 mg cholesterol; 5 g sugars; 0 g added sugars; 594 IU vitamin A; 10 mg vitamin C; 87 mg calcium; 1 mg iron; 317 mg sodium; 405 mg potassium