Boil up about 4 litres of water, spices and onion. Cook the meat in it at medium heat for about 3 hours. Wash the plums. Cook with 1/2 litre water, cinnamon stick and lemon for 20 minutes.
Let it cool down. Mix egg, mustard, sugar, allspice and 2 teaspoons of breadcrumbs. Take out meat, cut off rind. Dab ham with kitchen paper. Spread with mustard mixture and sprinkle with remaining breadcrumbs.
Bake in the preheated oven (electric oven: 200 °C/ gas: level 3) for about 20 minutes. Arrange ham and plums on a plate. Red cabbage, apple compote and boiled potatoes taste good with it. Serve cool beer or a strong white wine.