As September begins, there are still a few things you can sow in the European garden. According to Charles Dowding in his book ‘Winter Vegetables’ early September is a good time to sow winter salads, with crops such as corn salad (veldsla in Dutch), winter purslane (winter postelein) or rocket (rucola) coming immediately to my mind, but you could also try out mizuna. Endive (andijvie) can also be planted in early September but you will likely get smaller plants unless the plants overwinter (work with baby plants from a nursery not seed at this stage of the year).
Charles also recommends sowing some broad beans (tuinbonen) early in September. You can use the tender younger leaves in salads into the winter, and if the winter is mild then they may survive to give you beans in the early spring. If they are killed by frost then (being nitrogen fixing plants) they will at least have done your soil some good. I have done this myself and found in a city garden where the temperatures are moderated by the heat of the city my crop survived beautifully to bound into fruit quickly in the spring.