Place a large non-stick frying pan over high heat.
Add the oil, garlic, salt, and pepper, and saute until fragrant.
Add the mushrooms and coat in the mixture.
Continue stirring the mushrooms and add the butter 1 tablespoon at a time, allow each to melt and coat the mushrooms before adding the next.
Once the mushrooms have started to release liquid, reduce the heat to medium and stir occasionally until all the liquid has evaporated and the mushrooms have turned a deep brown color (it will take 10-15 minutes).
Remove from the heat and mix through the parsley before serving.