For the beef: Preheat the oven to 400 degrees F/200 degrees C. Drizzle the beef with the oil and sprinkle with salt and pepper. Weigh the meat and roast it for 12 minutes for the first pound and 10 minutes for each additional pound. (For 2 pounds/1 kg, about 25 minutes.) Remove from the oven and let sit at least 10 minutes before slicing.
For the remoulade sauce: Whisk together the mustard, anchovy paste, vinegar and egg yolk in a bowl. Add the olive oil, drop by drop, whisking constantly. Whisk in the peanut oil. The mixture should be very thick. Stir in the gherkins, capers, tarragon, chervil and parsley. Adjust the quantities of any of these to suit your taste. Grind in some pepper. Taste, and adjust the seasonings with salt and squirts of lemon juice.
Serve the remoulade sauce spooned over the beef.