Crack the peppercorns with a mortar and pestle
Melt butter in frying pan
Add shallots and peppercorns
Sauté for a minute or so, stirring, until the shallots begin to brown.
Add stock and bring to a brisk simmer.
Add Cognac and continue to simmer until reduced by half, 3 to 4 minutes.
Stir in crème fraîche and cook until sauce is lightly thickened.