In a small saucepan, melt 1 Tbsp of the butter and simmer the green peppercorns in it for 3-5 minutes. Add the cognac and burn all the alcohol off. This will flame up unless you have burnt the cognac earlier. Do not do this if you do not have adequate ventilation.
Stir in the mustard and add the demi-glaze and cream.
Season with salt and pepper to your taste.
Bring the sauce to a simmer and let simmer for 10 minutes or so then add the remaining 1 Tbsp of butter and serve over grilled steaks or grilled salmon.
***When buying demi-glaze, buy Demiglace Gold or equal substitute and follow the directions on the package to make it