• Preheat the oven to 240°C/220°C fan/gas mark 9.
• Halve the potatoes, quartering larger pieces, and pop onto a lined baking tray.
• Drizzle with oil and season with salt and pepper. Spread out in a single layer.
• Roast on the top shelf of the oven until fork tender, 25-35 mins.

• Meanwhile, halve, peel and chop the shallot into small pieces.
• Pick the tarragon leaves from their stalks and finely chop (discard the stalks).
• Take one egg (per 2P) and separate the yolk from the white (you can use the egg white later).

TIP: You'll be using the egg yolk raw, so use very fresh eggs to make the sauce.

• Place a small pot over medium-high heat with 2 tbsp butter (per 2P). 
• Add the shallot and cook for 2-3 mins.
• Add the tarragon and cook for 2 mins more. Remove the pot from the heat.
• Meanwhile, make a dressing with half the vinegar and a drizzle of oil.
• Just before serving toss the salad leaves with the dressing and season to taste with salt and pepper. 

• Place a large pan over high heat with a drizzle of oil. Season the beef with salt and pepper.
• Once hot, fry the beef until browned, 1-2 mins each side for medium-rare. 
• Cook for another 1-2 mins on each side if you like it medium and a further 1-2 mins on each side if you want it well-done. IMPORTANT: Wash hands and equipment after handling raw meat and its packaging. Meat is safe to eat when the outside is browned.
• Once cooked, transfer to a board and allow to rest.

• Add the egg yolk, half a mustard sachet (per 2P) and remaining vinegar to the pot with the shallot.
• Return the pot to low heat (as low as possible so as not to cook the egg yolk) and mix vigorously for 2-3 mins until the sauce thickens.
• Remove from the heat and stir in 1 tbsp water (per 2P) and a good drizzle of oil.
• Add a splash of water the sauce is too thick, you want a smooth sauce that coats the back of a spoon. Season to taste with salt and pepper.

• Thinly slice the beef.
• Divide the potatoes and sliced beef between plates.
• Pour the tarragon sauce over the beef.
• Serve with salad alongside.