In a large skillet, cook garlic in butter over medium-low heat, stirring until light golden. Add onion to garlic-butter mixture and cook, stirring until softened. Add mushrooms and sauté mixture over medium-high heat, stirring until onions are translucent and mushrooms are lightly browned, approximately 5 minutes. Stir in wine and cook until reduced by about half.

In a separate skillet, heat oil over medium heat. Add gluten free flour, stirring in small circles with a wooden spoon to incorporate. To avoid scorching, stir constantly until thickened and the gluten free roux is milky-tan in color.

Add stock to roux, whisking to prevent lumps.

Reduce heat to medium-low and stir periodically to prevent scorching. Cook down for 5 minutes to thicken.

Stir in mushroom-wine mixture and cook another 5 minutes over medium heat. Add more stock to thin the gluten free gravy, if necessary. Season with pepper and salt, to taste.