Using the whisk on a hand mixer, beat the butter, lime zest, lime juice and salt until light and creamy, shape into a rectangle on a board lined with cling film, cover and chill for approx. 1 hr.
Place a steamer basket in a wide pan, fill with water to just below the bottom of the basket. Add the vegetables, cover and cook over a medium heat for approx. 20 mins. until soft. Heat the cream, remove the pan from the heat. Pass the vegetables through a food mill and into the cream, season.
Heat the butter in a non-stick frying pan. Reduce the heat, fry the scallops over a medium heat for approx. 2 mins. on each side, season. Plate up the celeriac puree, top with the scallops and lime butter.