01 -
Preheat the oven to 375 degrees F. Grease a 9 x 13-inch baking dish and set aside.
02 -
Bring a large pot of salted water to a boil. Add the green beans and blanch them for 3 to 4 minutes. Drain, and immediately place them into a large bowl filled with ice water to stop the cooking process. Drain again and place the green beans on a clean kitchen towel or plate lined with paper towels to dry.
03 -
In a large skillet, melt 2 tablespoons of butter. Add the mushrooms, salt, and pepper. Cook for about five minutes, stirring occasionally. Add the minced garlic and cook for another two minutes until fragrant.
04 -
Sprinkle the flour over the mushrooms and stir until well combined. Pour in the vegetable broth and simmer for 2 to 3 minutes. Reduce the heat to medium-low and add the heavy cream. Cook, stirring occasionally, until the sauce has thickened, about 5 to 10 minutes.
05 -
Remove the skillet from heat and add the blanched green beans and 1 cup of fried onions. Stir until everything is well coated in the sauce. Pour this mixture into the prepared baking dish.
06 -
In a medium skillet, melt the remaining tablespoon of butter. Add the panko breadcrumbs and cook until they're golden and toasted, about 3 to 4 minutes. Season with a pinch of salt and pepper to taste.
07 -
Sprinkle the remaining cup of fried onions, the toasted breadcrumbs, and grated parmesan cheese over the green bean mixture. Bake uncovered for 20 minutes or until the casserole is hot and bubbly.
08 -
Remove from the oven and serve hot as a delicious side dish!