Place potato in a saucepan of cold, salted water, bring to the boil, then cook over medium-high heat for 10-12 minutes until tender. Drain and cool.
Meanwhile, for the pesto, place rocket, pine nuts, chives and lemon juice in a small food processor and whiz to combine. With the motor running, add the oil in a slow, steady stream until a coarse pesto. Season and set aside.
Transfer the potato to a bowl and roughly mash with a fork or potato masher. Add the mustard, chives and beaten egg. Season with salt and pepper and stir to combine. Fold through the ham. With damp hands, form the potato mixture into 18 even patties, about 2cm thick. Lightly dust in flour.
Add 2cm oil to a frypan and place over medium heat. In batches, cook potato cakes for 2 minutes each side or until golden and warmed through. Remove with a slotted spoon and drain on paper towel.
Toss the rocket with the pine nuts and preserved lemon rind, then serve with potato cakes, rocket pesto and lemon wedges.