Preheat the oven to 180°C. Line a baking sheet with parchment paper.
Unroll the pastry, then cut out round or square tarts (about 8cm), using scone or other cutters.
Mix the sauce together and spread it onto the tartlets, not going over the rim (you can create a rim using a smaller cutter).
Arrange half of a Parma ham slice on top of the tarts, then scatter the cheese on top.
Bake in the oven for 10-15 minutes until the rim is golden and the cheese has melted.
Meanwhile dry-fry the walnuts.
Scatter the walnuts all over the tarts just before serving.