Bring the wine and stock to a boil in a large shallow pan. Break 4 eggs, one by one, into the pan where there are the most bubbles (the bubbles will spin the eggs). Reduce heat, and poach eggs in until the yolks are fairly firm but still soft to the touch, 3 to 4 minutes. Remove with a slotted spoon to paper towels to drain. Trim any stringy edges off the eggs with scissors. Set aside. Repeat with remaining 4 eggs.
Prepare bouquet garni: Place bay leaf, thyme, parsley, and peppercorns on square of cheesecloth; tie with kitchen twine.
Add the onion, carrot, celery, garlic, bouquet garni, and peppercorns to the poaching liquid, and simmer until reduced by half, 20 to 25 minutes.
Meanwhile, melt 1 tablespoon butter in a medium saucepan, add mushrooms, and saute until tender, 2 to 3 minutes. Remove mushrooms, add bacon, and fry until brown. Drain bacon on paper towels. Add onions, and saute until brown and tender, 10 to 15 minutes. Drain off all the fat, replace the mushrooms and bacon, and set aside.
Heat oven to 350 degrees. Make the croutes: Using a round cutter, cut the bread into eight rounds just larger than the poached eggs. Brush rounds on both sides with oil, and bake them, turning them halfway, until they are evenly browned, 10 to 15 minutes. Set aside.
To thicken the sauce, crush the remaining 2 tablespoons butter on a plate with a fork, and work in the flour to form a soft paste. Whisk this mixture, a bit at a time, into the simmering wine mixture until it becomes thick enough to lightly coat a spoon. Strain the sauce into the pan with the mushrooms, onions, and bacon, pressing the vegetables in the strainer to extract all the liquid and flavor. Bring the sauce to a boil; season with salt and pepper.
Reheat eggs by immersing them in hot water for 1 minute. Set the croutes on warm plates. Drain the eggs on paper towels. Set one egg on each croute and spoon over the sauce.