Preheat oven to 400 degrees F.
Wash mushrooms, remove stems, and cut into small pieces (about 1").
Melt the butter, then add the olive oil, minced garlic, salt, and pepper. Stir until combined.
Next, add the chopped shiitake mushrooms to the garlic butter mixture.
Mix well and dump into a lightly sprayed 8x8 inch baking pan.
Stir once or twice while baking.
Roast the mushrooms for 22 to 24 minutes, or until tender.
Remove from oven and serve hot.
Leftovers can be stored in your fridge for a couple of days.
