Peel onions and cut them into fine rings. Fry with brown sugar in a pot for about 5 minutes while stirring. Deglaze with port wine and boil down in a jelly-like manner for about 40 minutes. Season onion jam with salt, pepper and vinegar and let it cool down.
Season minced beef with 1 1⁄2 tsp salt and 1 tsp pepper. Form approx. 30 mini rissoles from it. Heat the oil in a large pan. Fry the meatballs in it in portions on each side for about 3 minutes. Drain on kitchen paper.
Clean and wash the arugula, shake dry. Quarter cheese slices. Cut open rolls and cover with rocket, onion jam, meatballs and 2 quarters of cheese each. Possibly get stuck.
1⁄4 l milk and 1⁄8 l water lukewarm, remove from the stove. 1⁄2 Crumble the yeast into the cubes and dissolve them. Place 600 g flour, 1 teaspoon salt, 1 tablespoon sugar, 50 g butter and 1 egg (size M) in a mixing bowl. Add yeast milk and knead with the dough hooks of the mixer to a smooth dough. Cover and leave to rise in a warm place for about 45 minutes.
Knead the dough onto some flour. Form about 30 small rolls from the dough and place them on baking trays lined with baking paper. Cover them and let them rise for another 20 minutes. Whisk 1 egg yolk (size M) with 2 tbsp. milk. Spread the bread rolls with it. Sprinkle with 2 tbsp. sesame seeds. Bake in the preheated oven (electric oven: 200 °C/circulating air: 175 °C/gas: see manufacturer) one after the other for about 15 minutes. Let them cool down.