Rump steak has lots of flavour for a lower price than fillet or sirloin. Look for a good ratio in the marbling of fat to meat. The longer the beef is hung, the more its moisture disappears and the flavour develops.
Preheat the oven to 200°C/ fan 180°C/gas mark 6. Trim off the tops and bottoms from the beetroot. Cut into 4cm-thick slices then, using a 7–8cm pastry cutter, cut the slices into rounds. Lay in the middle of a large piece of greaseproof paper (30cm x 50cm) on a baking sheet. Pour over the melted butter and red wine vinegar, and sprinkle with the sugar and thyme sprigs. Season with salt and pepper. Fold each edge of the greaseproof paper over to form an envelope and fold over the edges again to seal, then bake in the preheated oven for 30 minutes or until tender.
Place the vinegar, tarragon sprig, shallot and peppercorns in a small saucepan on a medium to high heat and reduce until you are left with a third of the original liquid. Remove the tarragon.
Clarify the butter by melting it slowly in a small pan. Skim off any froth then carefully pour off the clear golden liquid, discarding the milky solids at the bottom.
In a heatproof bowl, break down the egg yolks by beating with a fork and stir in the tarragon vinegar reduction. Place the bowl over a pan of simmering water making sure the bowl doesn’t touch the water and, whisking all the time, slowly pour the clarified butter into the egg yolk mixture until you have a smooth, thick sauce. Stir in the garlic, chopped tarragon and chervil. Check for seasoning, adding salt, pepper and lemon juice if needed. Keep warm. Add a touch of warm water if the sauce becomes too thick.
Drizzle the steaks with rapeseed oil and use your fingers to coat well. Season with salt and pepper. Heat a large heavy-based frying pan. Once it is really hot, place the steaks in the pan, then sear over a high heat, without moving them, for 2–3 minutes, depending on how thick they are and how rare you want to serve them. Turn and cook on the other side. To test when done, use your finger or the back of a fork. Rare steaks will still feel springy, medium-rare steaks will still have a bit of give, and well-done steaks will feel firm, with no give to them.
Lift the steaks from the pan and let them rest for 5 minutes before serving with the baked beetroot and herb sauce.
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