Smash green peppercorns on a cutting board with the side of a knife. Add to small bowl and mix with the coarse black pepper. Smear peppercorns on both sides of all 6 steaks. In a large saute pan over high heat, add oil. Sear steaks for 4 minutes on each side, until well caramelized and peppercorns begin to crust. Remove from pan.
Add shallots to pan to caramelize while scraping the bottom. Add the flour and cook for 3 minutes while stirring until pasty, making a roux. Remove pan from flame. Add the brandy. Add the beef stock and heavy cream. Stir. Allow to simmer and cook until sauce thickens.
Drizzle steaks with sauce and garnish with parsley.