Preheat the oven to 350 degrees F and melt butter in a skillet over medium heat.

Add sliced mushrooms to the skillet, cook until browned and reduced by half, about 5-7 minutes.

In a small saucepan, heat the condensed soup over medium heat, stir in heavy cream, and adjust seasoning.

Combine the soup mixture with the mushrooms, then pour half into a 2-quart baking dish. Top with drained green beans and the remaining soup mixture.

Bake for 20 minutes, add fried onions on top, and bake for another 5-10 minutes until bubbly. Let cool before serving.