Heat the oil in a frying pan, sauté the onion for approx. 3 mins. Add the aubergines and sauté for approx. 5 mins. longer. Add the stock and simmer for approx. 10 mins., stirring occasionally, until the stock has been absorbed completely. Let cool, add the ricotta and salami and season.
Halve each roll of dough lengthwise. Take one half and brush with a little egg. Halve the aubergine mixture, separate into 6 walnut-sized portions and distribute on the dough. Lay the other half of the dough roll on the first half, press gently to seal, pressing out any air trapped in the ravioli, and cut the ravioli apart using a knife. Repeat using the remaining dough roll. Cook the ravioli in barely simmering salted water for approx. 5 mins. Remove with a slotted spoon, drain.
Melt the butter in a frying pan until it foams and smells slightly nutty, then add salt. Arrange the radicchio with the ravioli on plates and drizzle with the butter.