If not already tied, tie kitchen string around steaks to make nice rounds.

Cut stems from mushrooms (reserve for stockpot); slice caps. Thinly slice white and light green parts of onions; set aside. Slice dark green parts to make 2 tbsp/30 mL; set aside.

Coarsely grind peppercorns, then spread on plate; roll each steak in peppercorns to coat. In cast-iron or heavy-bottomed skillet over medium heat, add just enough oil to thinly coat bottom; cook steaks, turning once and sprinkling with salt halfway through, until desired doneness, about 6 minutes for rare or 8 minutes for medium.Transfer steaks to warmed platter and remove string; tent with foil.

Discard fat from skillet, then melt butter; add mushrooms and white and light green parts of onions and sauté until mushrooms are limp, about 2 minutes. Add brandy and cook until liquid is evaporated; stir in oyster sauce and cook for 1 minute. Stir in 2 tbsp/30 mL water; cook until moist but no liquid pools in bottom of pan. Stir in cream; cook, stirring, until thickened into sauce, about 1 minute. Stir in green parts of onions; spoon over steaks.

Makes 4 servings.