Cook the potatoes

• Place the potatoes in a saucepan, cover with cold salted water and bring to a simmer.
• Cook until a knife slides in with no resistance, then drain and let steam dry.

Make the pomme purée

• Pass the potatoes through a sieve or mash them until completely smooth.
• Warm the milk and fold it in, then beat in the cold butter a little at a time.
• Season with salt and keep warm.

Start the bordelaise

• Sweat the shallots in a little butter until soft and translucent.
• Add the red wine, thyme and garlic and reduce by two thirds.
• Pour in the beef stock and reduce again until lightly syrupy.

Finish the sauce

• Strain the sauce into a clean pan and discard the aromatics.
• Whisk in the poached bone marrow and a knob of butter off the heat.
• Season with salt and pepper and keep warm.

Sear the steak

• Pat the steak dry and season generously with salt and pepper.
• Sear in a hot pan with the neutral oil until deeply browned on both sides.
• Add butter, garlic and thyme and baste continuously.
• Rest the steak on a rack before slicing.

Plate

• Spoon the pomme purée onto warm plates.
• Slice the rested steak against the grain and lay it over the purée.
• Spoon the bordelaise over the steak and serve.