Onglet steak with celeriac and horseradish purée

Method

1. Melt the butter in a large pan. Finely chop the onion and garlic, then fry over a low heat for 5 minutes or until softened. Meanwhile, clean, peel and chop the celeriac into small chunks, then add to the pan and fry for 2 minutes. 
2. Pour in the cream and milk, then gently simmer for 20 minutes or until the celeriac is soft. When 10 minutes of the cooking time remain, heat a griddle pan until smoking. Cut the onglet steaks in half widthways, rub with olive oil and season, then griddle for 2-3 minutes on each side for medium-rare. Remove to a board to rest. 
3. Whizz the celeriac mixture in a blender until smooth. Transfer to a bowl, stir in 1 tbsp grated fresh horseradish and season. Slice the steaks, then serve with the purée, scattered with extra grated horseradish, and some blanched kale, if you like.