Make sure the meat is really cold. Slice the meat thinly, each slice about as thick as a pound coin, then lay them one at a time between two sheets of clingfilm. Bat them gently with a rolling pin until they are very thin.
Peel off the clingfilm and place the meat in a single layer on a large serving plate. Cover with clingfilm and put it back in the fridge.
Put the egg yolks, a little salt, the mustard and lemon juice in a blender then pour in enough olive oil to make a thin emulsion. You will need something like 75-100ml of oil.You can also make this dressing by hand using a bowl and a small whisk.
Drizzle the sauce over the meat, scatter the capers. Serve immediately.