To make the chutney, melt the butter and sauté the plums for 2-3 minutes. Add the sugar and vinegar and simmer for 15-20 minutes until the plums are soft and the sauce is rich and sticky.
Drain and cut each cheese in half. Wrap each piece in a slice of ham and secure with wooden cocktail sticks.
Heat half the olive oil in a non-stick pan until very hot. Season the wrapped mozzarella and fry for a few minutes on each side to brown and crisp the ham.
Place the salad leaves in a bowl with the remaining olive oil, the vinegar and some seasoning, and mix. Divide between two plates in a high pile.
Remove the mozzarella from the pan once the speck is nice and crisp, and place on top of the salad. Sprinkle with the toasted sesame seeds and pour over the juices remaining in the pan. Serve with the mixed leaves and a generous spoonful of plum chutney on the side.