Method

• 1.
  For the pastry, place the Jatz in a food processor and whiz until finely chopped. Place in a bowl with flour and 1 tsp salt flakes and stir to combine. Add the butter and toss to coat. Using your fingers, roughly rub in butter, leaving some big pieces of butter. Combine vinegar and 1/3 cup (80ml) iced water in a jug. Add to flour mixture, stirring to combine. Turn out onto a clean work surface and gently knead until the dough comes together. Enclose in plastic wrap and chill for 2 hours.

• 2.
  Preheat oven to 200°C/180°C fan-forced. Roll out pastry on a lightly floured work surface to 5mm thick. Place pastry into a 26cm tart pan, pressing into the fluted edge, and trim excess pastry. Chill for 20 minutes.
• 3.
  Spread mustard over pastry base and scatter with half of the cheese. Place potato in a bowl with oil and paprika, season. Place potato in a single layer over the top of the cheese. Top with ham and remaining 125g cheese, and scatter with pickled onion
• 4.
  Place on a baking tray and bake for 30 minutes. Reduce oven to 180°C/160°C fan-forced and bake for a further 15 minutes, or until deep golden. Cover with foil if it’s browning too quickly.
• 5.
  Serve tart with piccalilli pickles and topped with herbs.