Put 3 teaspoons of the peppercorns in a zip-top bag and crush them with a rolling pin, or use a mortar and pestle. Stop when you have coarse, irregular pieces with some texture, not a fine powder.

Set a frying pan over medium heat and add the butter and sunflower oil. Wait until the butter has melted and begins to foam lightly.

Add the shallots, salt, crushed peppercorns, and the remaining 1 teaspoon whole peppercorns, then cook for 2 to 3 minutes. Stir often until the shallots look softened and the peppercorns crackle gently without darkening.

Pour in the brandy and let it bubble for 1 minute, then add the beef stock and Worcestershire sauce. Bring the liquid to a boil and simmer rapidly for 5 minutes, until it has reduced by half and the sharp alcohol vapor smells sweeter.

Stir in the double cream and any juices collected from resting steak, if using, then return the sauce to a gentle simmer. Turn off the heat when the sauce coats the back of a spoon in a thin, glossy layer.

Spoon the warm sauce over steak. The peppercorns should remain distinct, with a velvety sauce that flows rather than sits in a thick mound.