Combine the ketchup, mayo, Worcestershire sauce, 2 tsp lemon juice and the Tabasco. Season to taste with a pinch of celery salt, if using, and black pepper, adding a splash more lemon juice, if needed. Mix the shallots with the remaining lemon juice and a pinch of salt in a non-metallic bowl and set aside to pickle lightly for 10 mins.

Heat the butter and nduja in a saucepan over a medium heat, swirling the pan until the butter melts. Once foaming, stir in the prawns and cook, basting them in the butter, until the prawns turn pink and are cooked through, about 3-4 mins. Remove from the heat and leave to cool slightly.

Spoon 1 tsp of the cocktail sauce into each lettuce leaf cup, then top with the prawns, some of the leftover nduja butter, the pickled shallots and parsley.