Preheat your oven to 350°F (175°C).

In a large skillet, melt butter or heat olive oil over medium heat. Add chopped onions and cook for about 3-4 minutes until translucent.

Stir in sliced mushrooms and sauté for about 5-7 minutes until golden brown.

Reduce heat, pour in heavy cream, and add salt and pepper. Simmer for 3-4 minutes.

Transfer the mixture to a greased baking dish, spreading it evenly.

Sprinkle shredded Guerrilla cheese over the mixture.

Bake in the preheated oven for 20-30 minutes until bubbly and golden brown.

Let cool for 5-10 minutes before serving.