This recipe for the classic French Onion Tart is from ” Lulu’s Provencal Food” by Richard Olney.
Sift the flour and salt into a mixing bowl, add the butter, and crumble the flour and butter together, lightly and rapidly, picking up portions and rubbing loosely between thumb and fingertips. Above all, don’t overwork the pastry.
Gather it together with a fork and a little cold water, wrap it in plastic, and refrigerate for at least 1 hour before rolling it out.
Warm 2 tablespoons olive oil in a large earthenware poêlon or heavy saute pan, add the onions and salt, and cook, covered, over very low heat, stirring occasionally with a wooden spoon, for an hour or more, or until they are so soft as to form a semi-puree.
Remove the lid and continue to cook until much of the liquid has evaporated; the onions should remain absolutely uncoloured. Season with pepper.
Preheat the oven to 190C/gas mark 5. With the palm of your hand, flatten the ball of pastry on a generously floured marble slab or other work surface, sprinkle over plenty of flour, and roll it out to a thickness of approximately 3mm.
Roll it up on the rolling pin and unroll it onto a large baking sheet. Roll up the edges and crimp them, either with your thumb, dipped repeatedly in flour, or with the tines of a fork.
Spread the onion puree evenly over the pastry, press the anchovy fillets into place in a simple design – latticework or wheel spokes – and push the olives into the puree to complete the design.
Dribble olive oil over the surface and bake for about 30 minutes, or until the edges of the pastry are golden and crisp. Serve hot or tepid, cut into small squares if serving with an aperitif or large wedges as a starter.