In a small saucepan, combine the Bordeaux wine and both types of peppercorns. Bring to a simmer over medium heat and reduce the wine by half, about 10-15 minutes.
In a separate skillet, melt the butter over medium heat. Add the chopped shallot and sauté until translucent, about 3-4 minutes.
Once the wine has reduced, strain it through a fine mesh sieve into the skillet with the shallots, discarding the peppercorns.
Stir in the Dijon mustard and Worcestershire sauce. Allow the sauce to simmer for an additional 5 minutes, stirring occasionally, until it thickens slightly.
Season with salt to taste and remove from heat.
Serve the sauce warm over your favorite steak, garnished with fresh parsley.