In a large saucepan, cook the bacon strips over moderately high heat until they begin to crisp. Pour off all but 2 tablespoons of the bacon fat. Add the chopped onion, chopped celery and diced potatoes and cook, stirring frequently, until the vegetables begin to soften, about 4 minutes. Add the butter and shiitake mushrooms and cook for 2 minutes. Stir in the flour and cook for 1 minute. Add the chicken stock, white wine, clam juice and heavy cream and bring to a boil. Reduce the heat, cover and simmer the chowder until the potatoes are tender, about 10 minutes.