Using a food processor, briefly mix the flours and salt. Add the butter and pulse until the mix resembles breadcrumbs.
Add the water and pulse until the dough just comes together (do not overmix). Divide the dough into four equal portions and roll out into rough circles on a floured surface. (Using a chilled bottle of water or wine for rolling is useful, as it keeps the pastry cool.)
Place the pastry rounds on a baking tray lined with baking paper.
To make the filling
Toss the apple slices with the sugar and cinnamon and arrange them in a fan in the centre of each pastry round, leaving a little space around the edge of each pie. Fold the edges of the pastry inwards. Brush the upturned edges of each one with melted butter.
Chill in the fridge while you preheat the oven to 200C.
Bake for 45 minutes, loosely covering the tarts with foil about 20 minutes into the baking time to prevent overbrowning.
To make the salted caramel
dissolve the sugar in a heavy-based pot. (Be extremely cautious here, as molten sugar can burn you if it comes in contact with your skin.
As soon as the sugar has dissolved, remove it from the heat.
Add the butter in parts while whisking continuously.
Return the pot to the heat and add the cream, still whisking vigorously.
When the sauce is smooth and well-combined, remove it from the heat, add a pinch of salt and stir to dissolve. Allow it to cool completely, then stir in another sprinkle of salt but do not let it dissolve – the crunchiness adds texture.Taste it and add more salt if desired.
To serve, drizzle the salted caramel over the warm apple tarts.
Notes
Leftover salted caramel can be stored in sterilized jars for weeks.