Wild Mushroom Whole Wheat Stuffing with Tarragon

loaves whole wheat bread (3 pounds), cut into 1-inch cubes

unsalted butter

thickly cut bacon or speck, cut into 1/4-inch dice

celery ribs, cut into 1/4-inch dice (2 cups)

large white onion, cut into 1/4-inch dice

garlic cloves, minced

mixed wild mushrooms, such as chanterelle, oyster and hen-of-the-woods, thickly sliced

finely chopped flat-leaf parsley

finely chopped tarragon

snipped chives

Turkey Stock

Salt and freshly ground pepper