Wash the plums, dab dry, halve and stone them. Cut the flesh into slices. Heat the fat. Add plums and lemon peel and steam for about 2 minutes while stirring. Add 3 tablespoons of sugar and cinnamon and toss briefly. For the froth, place the eggs, remaining sugar and advocaat in a metal bowl and whisk until frothy on a hot water bath with the whisk of the hand mixer. Spread the plums with foam sauce on four dessert plates