For the caramelized onions, peel the onions, halve them and cut into fine strips. Heat the oil in a large pan. Fry the onions in it over medium heat until soft, but do not brown.
Add sugar, vinegar and 2 tablespoons of water, bring to the boil and simmer for about 10 minutes, stirring from time to time. Leave to cool.
Grate the cheese roughly. Wash the chives, shake dry and cut into fine rolls. Line a baking tray with baking paper. Preheat the oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer).
Sift both types of flour and baking powder into a bowl. Add 1 teaspoon salt, butter in pieces, egg, each 1⁄3 cheese and chives. Add buttermilk, except 4 tbsp. for spreading. Knead with the dough hooks of the mixer to a soft, smooth dough.
Roll out the dough between two layers of baking paper to a rectangle (approx. 30 x 40 cm). Cover evenly with the onions, leaving an approx. 2 cm wide edge on one long side. Spread the remaining cheese and chives on the onions.
Roll up firmly from the other long side.
Place the roll on the baking tray and use a sharp knife to cut seven times deep but not through at regular intervals, creating 8 thick, continuous slices. Move them alternately a little to the right and left, so that the bread gets a zigzag shape.
Brush with remaining buttermilk and bake in a hot oven for about 40 minutes. Remove and let cool for about 20 minutes before serving. Pickled cucumbers and dips are delicious with it.