Start by pounding the steak with a mallet or rolling pin until it is around a third thinner and season well with salt.
Heat a pan in Roccbox until hot and add the oil. Add the seasoned steak to the pan and return to Roccbox to cook for around 4 minutes, flipping to ensure an even brown crust on both sides.
Add the butter, thyme and garlic to the pan until it begins to foam. Baste the steak with the butter and return the pan to Roccbox for a further 2-3 minutes, basting and turning as required.
Once cooked to your liking, remove the steak from the pan to rest and wipe the pan out with some kitchen towel.
Pop 40g of the butter into the pan and allow to melt. Add the shallot, half the picked thyme leaves and soften briefly in Roccbox. Add the brandy and flambé in the mouth of Roccbox. Add the beef stock and green peppercorns and return the pan to Roccbox to reduce by half.
Remove the pan from the heat and add the cream and stir in the remaining butter. Finish with the remaining thyme leaves and the lemon juice.
Carve the steak, check the seasoning on the sauce and serve.