Mix the flour, salt, sugar and yeast in the food processor bowl. Add the water, milk, egg and butter, knead for approx. 5 mins. to form a soft, smooth dough using the dough hook on a food processor. Cover the dough and leave to rise for approx. 1 hr. Divide the dough into 10 portions, shape into balls, flatten a little and place on a baking tray lined with baking paper. Cover and leave to rise for a further 1 hr.
Whisk the egg, water and milk. Brush the buns with the egg glaze. Sprinkle with the potato chips.
Approx. 18 mins. in the centre of an oven preheated to 200°C. Remove the buns from the oven, leave to cool on a cooling rack.
Heat the oil in a pan, add the onions and sweat for approx. 10 mins. Add the sugar, caramelize. Pour in the balsamic, simmer briefly, set aside.
Place the avocado in a bowl, mash with a fork. Mix in the quark and the remaining ingredients.
Season the meat, divide into 10 portions, shape into 10 burgers. Wrap each in a rasher of bacon. Heat the oil in a pan, fry the burgers for approx. 3 mins. on each side.
Slice the brioche buns crosswise, fill with the onions, burgers, sauce, feta and potato chips.