Start with the pastry. Rub the butter in with your fingers until you can no longer see it and the mixture changes colour and resembles breadcrumbs. It’s best to use cubes of cold butter, because butter releases more fat at room temperature. Add a pinch of salt and the egg yolk. Knead well to make a smooth dough. Wrap in clingfilm and put in the fridge for an hour.
In the meantime, sauté the pumpkin in a frying pan with a good dash of olive oil for about 5 minutes until crispy. It’s best to use a frying pan you can put straight into the oven. Arrange the pumpkin, cheese and walnuts tightly and evenly around the pan. Cover with the rolled-out pastry and bake at 180 ºC for half an hour. Invert and serve hot.