1. Prepare the Green Beans: Begin by steaming or boiling your fresh green beans until they are tender-crisp. You want them cooked through but still retaining a slight bite. This usually takes about 5-7 minutes for steaming or 3-5 minutes for boiling. Drain them thoroughly and set aside.

2. Saute the Aromatics: In a large skillet or oven-safe pan, heat the olive oil over medium heat. Add the chopped onion and cook until it softens and becomes translucent, which typically takes about 3-5 minutes.

3. Add Mushrooms and Garlic: Stir in the sliced mushrooms and cook for another 5-7 minutes, or until they release their moisture and start to brown. Then, add the minced garlic and cook for just one more minute until fragrant, being careful not to burn it.

4. Create the Creamy Sauce: Reduce the heat to low. Pour in the heavy cream and chicken broth. Add the softened cream cheese and stir continuously until the cream cheese is fully melted and the sauce is smooth and well combined.

5. Season and Combine: Stir in 1/2 cup of grated Parmesan cheese, salt, and black pepper. Mix well until the cheese is melted and incorporated into the sauce. Gently fold in the cooked green beans, ensuring they are fully coated with the creamy sauce.

6. Bake the Casserole: If your skillet is oven-safe, you can continue with it. Otherwise, transfer the green bean mixture to a 9×13 inch baking dish. Sprinkle the remaining Parmesan cheese and your chosen topping (keto-friendly crispy fried onions or crushed pork rinds) evenly over the top.

7. Finish in the Oven: Bake in a preheated oven at 375 F (190 C) for 10-15 minutes, or until the topping is golden brown and the casserole is bubbly around the edges. Keep an eye on it to prevent the topping from burning.

8. Serve Hot: Remove from the oven and let it stand for a few minutes before serving. This allows the sauce to set slightly and makes for easier serving.