Knead the flour together with the sugar, butter, egg and salt until obtaining a smooth dough.
Wrap it with some cling wrap and put it in the fridge for 30 minutes.
Take it out of the fridge, place it on a sheet of baking paper and roll it into a 1 cm – 0.4 inch thick rectangular sheet.
Cut a rectangle of approximately the same size as your tart tin and put the dough in the greased tin. Press it down well and make sure you have dough at the side as well.
Assembling
Peel the apples, cut them in quarters, remove the core and slice each quarter in 4 or 5 pieces. Place the apple slices on top of the dough, trying not to leave any gaps.
Sprinkle with the sugar and top with the chopped butter.
Bake in a pre-heated oven at 180°C – 355°F for about 35 minutes, or until golden brown and cooked through.
Brush with the Dulce de Leche and bake for another 5 minutes.
Let the tart cool down completely before un-moulding and serving it.