Reduce the heavy cream to sauce consistency in large saucepot. Use a wire whip to whisk while reducing to prevent boiling over.
In another saucepot sweat the shallots in a little oil, then add ⅔ of the green peppercorns and crush some of them with the backside of a large spoon. Stirring well to sauté just a bit, then flame with the brandy and continue to crush the peppercorns and reducing it a bit. Pour the reduced and thickened heavy cream through a fine strainer as you add it to the peppercorns.
Add the oyster liquor (for seafood preparations) and veal stock and then allow the sauce to reduce a bit to thicken over medium-low heat.
Using a burr-mixer blend the sauce until smooth and most of the peppercorns are puréed. Or transfer the sauce to a blender with the center cap removed and blend until smooth.
Strain through a fine sieve and season to taste with the salt and white pepper. Add the remaining ⅓ of the peppercorns to the sauce for garnish and stir.