To a large saucepan or deep skillet over medium heat, melt the butter.
Add in the sliced mushrooms and season with salt.
Simmer, stirring frequently, until wilted and liquid has evaporated, approximately 10-15 minutes. The mushrooms should be brown, but not black.
Add in the flour and cook, stirring frequently, another 5 minutes.
While briskly stirring, add in 1 cup of beef broth. It will slightly thicken and look creamy. Once incorporated, add in the remaining stock and stir until fully combined.
Season with black pepper and thyme.
Reduce the heat to medium-low and simmer until thickened, stirring frequently, for about 20 minutes.
Notes
For extra flavor, add 1 Tablespoon of sherry or apple cider vinegar with the beef broth.Any mushrooms, or combination of mushrooms, can be used.For thicker gravy, add 1 tablespoon of cornstarch to 3 tablespoons of the broth, mix, and return to simmer.Store leftovers covered in the fridge for up to 3 days.