Tie the thyme, parsley, and bay leaf into a bouquet with kitchen twine.
Put 2 tbsp (30 ml) broth in a large skillet, Dutch oven or stock pot see note) and heat on medium heat. When the broth begins to boil add the mushrooms, onion and carrots and cook for five minutes. Stir frequently and add a few more tbsp of broth if needed. Add the garlic and stir well. Cook for two minutes.
If you are cooking this in your slow cooker, transfer the onions, carrots, mushrooms and garlic from the pan to the cooker (if cooking in a stock pot or Dutch oven, leave the onions and add the potatoes and remaining ingredients) and add the potatoes, the remaining broth, 2 cups (480 ml) water, tamari or soy sauce, Worcestershire sauce, herbs, and salt and pepper. Gently push the herbs into the broth and bring to a boil. Reduce the heat to simmer and cook for one hour, or two or more hours in your slow cooker. The longer you cook the stew the softer the potatoes will become.
Melt the butter in a small saucepan on medium heat. When it's melted whisk in the flour until it's creamy and thick. Whisk in the milk until it's creamy and slurry. Stir it into the stew until it's completely combined and let it simmer for approximately ten minutes until the broth thickens. Remove the herbs. Taste and add more salt and pepper as needed.
If you can't saute the onions, carrots, mushrooms, and garlic in the slow cooker, saute them in a pan and then transfer them to the cooker to finish.