Onions peel, halve and in strips cut. Melt 2 tablespoons of butter in a saucepan. Stir-fry the onions for about 5 minutes over medium heat until soft. Add brown sugar and vinegar and simmer for about 5 minutes. Leave to cool.
Preheat the oven for the muffins (electric oven: 160 °C/circulating air: 140 °C/gas: see manufacturer). Grease the twelve troughs of a muffin tray. Finely grate the parmesan. Mix eggs, sour cream and parmesan. Season vigorously with salt and pepper. Spread the mixture into the hollows. Spread the onions on top and bake in a hot oven for 25
In the meantime, chop the olives for the Gremolata. Wash parsley, shake dry, pluck off leaves and chop coarsely. Peel garlic and chop very finely. Mix olives, parsley, garlic and lemon juice. Season to taste with pepper.
Take the muffins out of the oven and let them cool down for about 5 minutes. Then remove them from the trays and arrange them with the olive gremolata.