Heat thick-bottomed pot over low heat. Add olive oil and butter and melt.

Add mushrooms and onions, stir with wooden spoon and sweat until soft. (Note: It may seem like there is a lot of fat in the pot but the mushrooms will absorb it, and release water as well. This is needed for thickening the gravy.)

Add garlic, cook briefly and stir in dried thyme.

Add flour and mix until it soaks up liquid and forms paste-like consistency known as roux.

When roux is formed and hot, add ⅓ of the cold broth and stir quickly and well until combined.

Turn up heat under pot and stir in another ⅓ of broth. Stir well until combined.

Stir in last of the broth and combine well.

Whisk in fresh thyme, pepper and tamari. Taste and adjust seasonings. (Note: If gravy is not thick enough, continue to simmer. If gravy is too thick, add more mushroom broth.)