Preheat your oven to 350°F (175°C).

In a large skillet, heat a splash of olive oil over medium heat. Add diced onions and minced garlic, stirring until translucent, about 3-4 minutes. Then, add sliced mushrooms and cook for 5-7 minutes until softened.

In a mixing bowl, combine the sautéed mixture with sharp cheddar cheese and heavy cream, stirring until thoroughly mixed.

Pour the creamy mixture into a greased casserole dish and spread evenly.

Bake in the preheated oven for approximately 30 minutes, until the top is golden and bubbly.

Let it cool for about 5-10 minutes, then serve as a delicious side or main dish.