1. Peel the onions, finely slice them and put them in a large saucepan with the truffle oil. Cover and cook over low heat for 30 minutes.
2. Roll out the dough, add the onions, decorate with anchovies and olives.
3. Place in the oven, preheated, for 15 minutes at 190 degrees.
4. Add pepper when removing from the oven