For the “Fried” Onion Topping
- 1 tablespoon melted butter
- 1 medium yellow onion, thinly sliced
- 1/2 cup Panko breadcrumbs
- 1/4 cup grated parmesan
- 1 teaspoon garlic powder
- 1 teaspoon paprika
- 1 teaspoon salt
- 1/4 teaspoon black pepper
For the Casserole Filling
- 24 oz fresh green beans
- 2 tablespoons unsalted butter
- 3 cloves garlic, minced
- 16 oz sliced baby Bella mushrooms
- 1/2 tablespoon fresh thyme
- 1/4 cup flour
- 2 cups chicken broth
- 1/2 cup half and half
- 1/2 cup grated parmesan
- 1 teaspoon salt, plus more to taste
- black pepper, to taste