Preheat the oven to 375°F.
Heat a cast iron or oven-safe skillet over medium-high heat. Add two tablespoons of butter and the diced onions to the skillet. Allow the onions to sweat and get translucent and soft. Add the mushrooms and garlic, and saute until the mushrooms have browned.
4 tablespoon Salted butter, ½ Yellow onion, 2 cups Cremini mushrooms, 4 cloves Garlic
Lower the heat to medium-low. Add the remaining two tablespoons of butter to the skillet, and sprinkle in the flour. Combine, and cook the butter through for 2-3 minutes to get rid of the raw taste of the flour.
4 tablespoon Salted butter, 2 tablespoon All purpose flour
Stir in the chicken broth vigorously, to ensure there are no lumps formed with the flour. Combine until a sauce has formed, and season with the cajun seasoning, smoked paprika, salt and fresh thyme. Let the sauce simmer and thicken for 3-5 minutes.
2 cups Chicken broth, 2 teaspoon Sea salt, 1 tablespoon Fresh thyme, 1 teaspoon Tony's Cajun Seasoning, 1 teaspoon Smoked paprika
Once the sauce has thickened, lower the heat to low. Stir in the heavy cream and combine.
½ cup Heavy whipping cream
Toss in the green beans with the prepared sauce, and flatten into one uniform layer.
1 lb Green beans
Top the green beans with the french fried onions, and sprinkle with half of the shredded parmesan cheese. Bake the casserole for 20-25 minutes.
2 cups French fried onions, ½ cup Parmesan cheese
Finish the casserole with the remaining shredded parmesan cheese, and serve.
½ cup Parmesan cheese