Heat 1 tablespoon of the butter in a large pot over medium heat. Add the mushrooms and cook for 5 minutes. Remove from the pot with a slotted spoon. Add the remaining 1 tablespoon butter to the same pot over medium heat. Add the onion, celery, and garlic and cook, stirring occasionally, for 5 minutes, or until softened. Stir in the potatoes, bay leaves, dulse, thyme, Old Bay, salt, pepper, and vegetable broth. Bring to a boil and then decrease the heat to low and cook for 30 minutes, or until the potatoes are just tender. Remove the bay leaves and stir in the liquid smoke.