Preheat the oven to 350° and grease medium sized casserole dish with grass-fed butter.
Bring a large pot of water to a boil and add green beans. Boil for 3-5 minutes until they are crunchy soft. Remove beans from water and set aside.
Heat grass-fed butter in a medium saucepan over medium-high heat. When butter is melted, add onions. Sauté onions for 3 minutes, then add garlic and mushrooms.
Sauté mushrooms and garlic for another 3 minutes. Pour in chicken broth, scraping up any browned bits from the bottom of the pot. Reduce heat to medium and stir in cream cheese, Dijon mustard, cheddar, salt and pepper until cream cheese is melted.
Stir in green beans until coated, then turn off heat.
Spread mixture in prepared baking dish.
For the topping, place bacon cubes, Parmesan cheese and melted butter in a small bowl and mix through. Sprinkle the topping over the casserole.