Red onions caramelised in coriander and balsamic vinegar, immense. Roast them in chunks in the oven for 30 minutes with fennel bulbs, ground coriander seeds, balsamic and some olive oil, caramelise some sugar in a frying pan, dump the onion/fennel in the sugar, chuck in a ton of grana padano or parmesan cheese, stuck some puff pastry on top, give it another 20 minutes in the oven, and it will turn into this:
Tarte tatin, mitherfecker.