For the onion tart, knead a shortcrust dough from all the ingredients for the dough and press it into a greased tart mold.
While the dough rests for 1/2 hour, sauté the onion slices in olive oil until translucent, then add the caraway seeds and pour the onion mixture on top of the dough in the mold.
Mix finely ground spelt and chufas nuts with whipped cream and a little salt to make a mixture, pour it over the top and bake the onion cake at 180-200° Celsius for 30-40 minutes.