Heat a large skillet (I love using my 12 inch iron skillet) over medium heat. Once the skillet is warm, add the butter, olive oil, and sliced mushrooms.
Cook mushrooms until they are browned and soft stirring occasionally, about 5-7 minutes. Once the mushrooms are soft add the minced garlic and cook for an additional 1 minute until fragrant.
Add the flour to the skillet and stir until completely dissolved.
Add the half and half, fresh thyme, dried thyme, salt and pepper to taste. Turn heat up and bring sauce to a boil for about 1 minute, then reduce heat to low and whisk until slightly thickened, about 2 minutes.
Remove from heat and stir in grated Parmesan cheese (optional-for a thicker sauce) until smooth. Adjust seasoning to taste. Discard whole thyme sprigs and serve warm with recipe of choice, enjoy.
Leftover Storage: Store leftover sauce in an airtight container in the fridge for up to 4 days. Re-warm in the microwave for 30 seconds and at to recipe of choice (check in the post above for awesome recipe pairings)!Make it Vegan: If you want to make this mushroom sauce vegan you can easily do that by swapping the half and half out for a vegan milk alternative like soy milk. Also, you can use a vegan butter or just use olive oil in its place and leave out the cheese.Mushroom Options: Any mushrooms will do for this sauce recipe, and I would go with what is in season. I used pre-sliced baby bella mushrooms (my fave) for this sauce and it turned out great. You could get whole baby bella mushrooms and slice them yourself, shiitake mushrooms or Crimini mushrooms. Each mushroom has its own distinct flavor so using a different one will slightly change the sauce.Crush the Parmesan Cheese:I like to add in a bit of grated parmesan cheese for added flavor and to thicken the sauce. Before adding make sure there are no large clumps in the cheese so it is easier to whisk into the mushroom sauce. This step is optional and if you prefer a lighter sauce you can leave the cheese out.