1) Add olive oil to roasting tin after removing beef. Add shallots, garlic, and thyme and saute for 1 to 2 minutes.
2) Take off the heat, pour in brandy and flambe using a long kitchen match. After flame dies down, return to the heat, add stock and reduce by about half.
3) Strain out solids, then stir in cream and mustard.
4) Reduce by half again, then turn off the heat and add green peppercorns.