Ad the olive oil and butter to a large skillet set over medium-high heat.
Add the mushrooms to the pan, stir and saute for 4 to 5 minutes without disturbing.
Reduce the heat to medium and add the onion, garlic, salt, pepper and thyme. Cook for an additional 6 to 7 minutes, or until the mushrooms and onions are soft and nicely browned.
Season with salt and pepper to taste and serve as desired.
Notes
Substitutions: You can substitute the dried thyme with another herb like Italian seasoning, basil or herbs de Provence. You can also add bell peppers and saute until soft and fragrant.Storing: Refrigerate extras in a shallow, airtight container for 3-5 days.Freezing: Let cool, place in a freezer bag with as much air removed as possible, and freeze for up to 3 months. When ready to use your mushrooms and onions, they can be reheated from frozen directly in a pan over medium-high heat.