In a big bowl, we prepare the marinade. We add all the ingredients. The onion, the lemon juice and zest, the fresh herbs and the spices. We then add the steaks and marinate them gore a couple of hours.
In a tray, we add the unpeeled celeriac, cut in large pieces, the garlic, the onion, the olive oil, salt, pepper, and rosemary. We cook with our tray covered with craft paper in170oC for an hour. When ready, we mix the mascarpone cheese in a blender. We add more salt if needed and some lemon juice.
Green apple mash
In a small pot, we add some olive oil and start steaming apple cuts with a cinnamon stick and the brown sugar. We remove the stick and continue mixing in a blender.
We make a mix with the olive oil and the flour. We sieve all the liquids remained from the steak cooking and boil for three minutes.