To make the horseradish cream, whisk all the ingredients together with salt and pepper until spoonable, then set aside. Lay the slices of beef on four serving plates. In a bowl, mix the beetroot, shallot and salad leaves together. Dress with the sherry vinegar and 3 tbsp of the olive oil, then gently toss.
Neatly pile a mound of salad into the centre of each plate and scatter some microleaves around the outside. Top the salad with a neat spoonful of horseradish cream, drizzle with the remaining olive oil and serve.