In a small skillet, cook flour over medium-high high until it turns light brown, stirring constantly.  Transfer the flour to a plate to cool.  In a separate bowl, cover dried porcini mushrooms with boiling water and let steep for 20 minutes.  Strain mushrooms and reserve the soaking liquid.  Chop the porcinis.  Heat a Dutch-oven (or large soup pot) to medium-high, melt butter, and saute onion until tender.  Add thyme, garlic, salt, pepper and saute another 30 seconds.  Next add the shiitake mushrooms and cook for 3 minutes more.  Stir constantly.  Add button mushrooms and cook another 3 minutes, stirring constantly.  Incorporate the chopped porcinis and broth.  In a separate bowl,  combine reserved soaking liquid and toasted flour.  Stir with a whisk and add to Dutch oven.  Bring to a boil, reduce heat, and simmer for 15 minutes uncovered.  Add milk, simmer again for 10 minutes, stirring frequently.  Remove the Dutch oven from heat and stir in Sherry and half-and-half.  Remove 2 cups of soup from pan and pour into blender.  Process until the soup is smooth, then add back to the Dutch oven.  Warm the soup once more over low heat until thoroughly heated.  Serve and enjoy with a earthy Pinot Noir from Burgundy, France.