Brigitte's Sauerbraten

• 2 peppercorns
• 1 bayleaf
• 1/2 l buttermilk
• 1/2 l water
• 850 gr roast beef (boneless)
• 240 ml wine (red)
• 24 gr cornstarch
• 5 slices bacon
• 2 slices carrots
• 1 slice onion