Roll out the dough to a circle, about ¼ in / 0.5 cm thick, and arrange it half on and half off a floured baking sheet (the over-lapping half will be folded over the filling). Squeeze the meat from the sausages, and fry with the onion or shallot for 5 minutes. Spread tomato purée on the half of the dough on the baking sheet, leaving a ½ in / 1 cm border, and then put the sausage meat on top, then the slices of cheese and the anchovies, capers and olives, if you are using them, and finally the herbs and a few grindings of pepper. Moisten the border of dough with water, fold over the other half, pinch the edges together to seal, cover with a damp cloth, and leave to prove for 30 minutes. Bake in a preheated oven at 180°C / 350°F / Mark 4. Serve while hot.