Soak porcini in 1 cup warm water until softened, about 20 minutes. Lift porcini from liquid and coarsely chop; strain liquid through a cheesecloth-lined sieve and reserve.
In a large pot, heat oil over medium. Add leeks; season with salt and pepper and cook for 5 minutes or until tender.
Add garlic, porcini, and chopped mushrooms, season with salt and pepper, and cook for 7 minutes or until mushrooms just begin to brown. Add fennel seeds, bay leaves, tomato paste, and tomatoes, and cook for 3 minutes. Add marsala (if using), porcini liquid, and broth. Reduce heat to low and simmer for 30 minutes. Discard bay leaves before serving.