1 Tbsp grainy mustard
200g (7 oz) gruyere or Swiss cheese, thinly sliced
Freshly ground white pepper, optional
50g (1½ oz) thinly sliced prosciutto or mortadella
Extra virgin olive oil
¾ cup freshly grated parmesan cheese, optional
1 Roll each pastry sheet a few centimetres bigger on a floured surface on baking (parchment) paper. Cut one sheet into four squares (or triangles). Spread each square with mustard, not quite to the edges, then dampen the edges of each square with a little water. Put on a layer of cheese, a grind of pepper if using, then a layer of prosciutto or mortadella, and another of cheese. Use scissors to snip the cheese and meat to fit the pastry squares.
2 Cut the other sheet of pastry into four squares and put on top of the assembled pastry squares, then press edges to seal. Trim with a sharp knife to neaten if necessary or crimp the edges. If pastry is soft, chill pies until firm.
3 Preheat oven to 200°C (400°F). Brush pie tops lightly with extra virgin olive oil, then prick all over with a fork. Scatter with parmesan or sprinkle with flaky sea salt. Bake for about 20 minutes, or until a good golden colour. Serve hot.
I used sliced Swiss cheese which made assembling the pastries very easy. I cut each triangle in half for serving.
The pies can be assembled ahead of baking: layer them in a container with baking (parchment) paper and cover with plastic wrap and keep them in the fridge until ready to cook. Finish off with the fork pricking and parmesan or flaky sea salt just before cooking.