{nut free + paleo + whole30 + dairy free}
Heat olive oil or ghee over medium high heat in a large skillet until shimmering. Add onions and mushrooms, and cook, stirring occasionally, until soft and caramelized, about 6-8 minutes.
Once it cools slightly it will thicken. If the gravy still seems too thin after cooling slightly, move it back to the skillet and simmer uncovered, stirring occasionally, until thickened to your liking.