Place a very large saucepan or crockpot over a low heat and add 2 tbs of the olive oil and add the shallots and fry until lightly golden, around 15 minutes. Add the carrots, garlic and celery and increase the heat to medium and cook until the carrots are golden. Remove from the saucepan and set aside.
Place the flour in a bowl and season with salt and pepper. Toss the portobello mushrooms in the flour. Add 2 tbs of olive oil to the saucepan and increase the heat to medium high and brown the mushrooms. You may need to do this in two batches depending on the size of your pan. When all the portobello mushrooms are browned reduce the heat to medium and add the wine, vegetable stock, bay leaves and thyme and bring to a simmer. Reduce the heat to low and simmer covered for 45 minutes, stirring occasionally.
Add the vegetables to the pan, along with the zucchini and button mushrooms and simmer for 30 minutes.