In a large pot, heat up the olive oil and add half of the mushrooms. Cook until nicely browned, then remove them from the pot and set aside.
To that same pot, add the 2 tablespoons of butter, garlic, onion, and remaining sliced mushrooms. Cook for about 5 minutes.
After that time has passed, turn off the heat and remove the lid. Add about 1 more tablespoon of butter (optional), the reserved browned mushrooms, and the parsley. Put the lid back on and let the Rice with Mushrooms rest for 10 minutes.
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