Put all the filling ingredients, except the semolina, into a saucepan, and bring gently to the boil. Stir in the semolina to thicken the mixture; about half should be sufficient. Cook the mixture for a few minutes. Let it cool, and then put to one side until required. If it is made the night before, covered and refrigerated, it is very easy to handle when cold.
Make the pastry by sifting the flour into a bowl and rubbing in the butter. Stir in the egg yolk and enough water to bind it. Divide the pastry into two or three pieces for ease of handling. Roll it out, and cut into rectangles 7 × 4 in / 18 × 10 cm.
Take a tablespoon of the filling, and roll it into a thumb-thick sausage shape, 7 in / 18 cm long. Use some of the remaining semolina to prevent sticking, if necessary. Place in the middle of one of the pastry rectangles and fold the pastry over to seal in the filling. Bring the two ends together to form a ring. Make the rest of the rings in the same way. As each one is made, place it on a baking sheet which you have first greased and scattered with some of the remaining semolina. With a sharp knife, make half a dozen slashes in the pastry on the top surface of each ring. Bake in the centre of a preheated oven at 180°C / 350°F / Mark 4 for 20 minutes. If your oven tends towards hot, use a lower setting, for the pastry should not brown. As it bakes, the filling expands and spills through the slashes, providing a striking black and white contrast.