To begin cook the potato in boiling salted water without peeling first. Once cooked, peel and finely dice. Finely chop the onion and sauté in a little olive oil until translucent. Cool both.
In a large mixing bowl, stir together the venison, cooled onion and potato, add the egg yolks, pickled beetroot and capers then season. Using your hands, shape the mixture into 4 large burgers or 6 small. Place in the fridge for 15 minutes.
Place the celeriac in a bowl, add the lemon juice, vinegar, mustard, mayonnaise and yoghurt and season. Stir well and then add the herbs and chilli, check the seasoning and leave to stand for 30 minutes.
In a large frying pan heat the butter and a little olive oil over medium to high heat. Add the burgers, flip once, cook until each side is a rich golden brown and the centre is cooked as you’d like. Serve with the celeriac remoulade.