In a skillet, melt the butter over medium heat.
Once bubbling, add the minced garlic to the pan and sauté for about 1 minute until it becomes fragrant.
Introduce the sliced mushrooms to the skillet, cooking and stirring occasionally until they are tender and golden brown, about 5-7 minutes. Season them with salt and pepper to your liking. Then, remove from heat and set aside.
In a separate skillet or griddle, heat it over medium heat. Spread a thin layer of butter on one side of each slice of bread.
Place two slices of bread, buttered side down, onto the skillet. On each slice, place a slice of cheese, and then divide the cooked mushrooms evenly between the two.
Top it all off with the remaining slices of bread, buttered side up.
Cook these sandwiches for 2-3 minutes on each side, until the bread turns golden brown and the cheese nicely melts.
After cooking, remove them from the skillet and allow them to cool for a minute or two before slicing. Serve hot and enjoy this scrumptious treat!