- 1 Tart pan
Mix butter with salt, egg, hazelnuts and flour and quickly knead into a smooth ball. Cover in plastic wrap and chill about 30 minutes in the refrigerator.
Peel and cube onions. Slice sage leaves into strips.
Add sugar and vinegar to a pot and stir in onions, raisins, sage, salt, cumin and pepper, and bring to a boil. Reduce heat and simmer uncovered for about 20 minutes. Stir occasionally.
Roll out dough on a floured surface until slightly larger than the tart pan. Prick the dough with a fork several times. Cut out remaining dough in the shape of small onions for decoration.
Line the bottom of the pan with parchment and bake the dough in a preheated oven at 200°C (approximately 400°F) for 15 minutes. Bake the decorative onion dough also on a small pan. Remove the tart crust, spread the onion mixture on the crust and bake for another 25 minutes. Garnish with the decorative onions and serve.