Using a pestle and mortar, crush the black, white and pink peppercorns gently. Place the crushed pepper in to a sieve and shake off any excess powder, keeping just the crushed peppercorns. Season the steaks all over with the crushed peppercorns, patting them in with your hands so they stick, then season with salt.
Heat a large well-seasoned sauté or frying pan over a high heat, then add a drizzle of oil. When it is hot, add the steaks and fry them for 3–4 minutes on each side until well coloured. This should give you medium-rare meat, which is how I like my steaks, but fry them for a bit longer if you like. Set aside to rest on a plate with a rim for 5 minutes, covered with kitchen foil, while you make the sauce.
Add the shallots to the oil remaining in the pan and sauté for 1–2 minutes until softened, but not coloured. Add the brandy, stirring to deglaze the pan, and boil until it evaporates. You can flambé the pan if you’re feeling adventurous, but it’s not necessary. Add the cream and bring to the boil, then add the cooking juices that have accumulated while the steaks were resting.
As the sauce thickens whisk in the butter, then add the parsley, mustard and green peppercorns. Adjust the seasoning with salt and pepper, if necessary. Add the steaks to the pan and baste them in the sauce, then serve.