Add olive oil to pan after removing beef. Add shallots, garlic, and thyme; saute for 1 to 2 minutes, then, off heat, add brandy and flambe using a long kitchen match. After flame dies down, return to the heat, add stock and reduce by about half. Strain out solids, then add 2 cups cream and mustard. Reduce by half again, then shut off heat and add green peppercorns.