1. Heat butter and oil in a large skillet over medium heat.
2. Season filets with salt and pepper.
3. Saute 5 minutes per side for rare (10 min for medium).
4. Transfer to a heated platter and keep warm.
5. To make the sauce, add brandy to same skillet.
6. Set aflame, shaking pan until flame dies.
7. Add shallots and stir on high heat for 2 to 3 minutes.
8. Rinse green peppercorns in cold water.
9. Drain and chop.
10. Add to pan with cream, mustard, and tarragon.
11. Boil on high heat 2 to 3 minutes, stirring until sauce thickens.
12. Add juice from filets.
13. Pour sauce over filets and serve.