Preheat the oven to 180C (160C fan, gas mark 4). Peel and slice the apples into quarters, then half each quarter to get eight slices from each apple.
Place the sugar, butter, water, lemon juice and salt in a frying pan and heat until the sugar has dissolved and the butter has melted. Keep stirring the mixture all the time.
Add the apples, covering the whole pan. Return to the heat and allow to bubble furiously for 10 minutes until the apples are nicely caramelised. While the apples are cooking, roll out the pastry so it is wide enough to cover individual tartlet tins. Divide the cooked apples equally among the tins and cover with discs of pastry, carefully tucking the edge inside the tins.
Bake in the oven for about 30 minutes – the pastry should be golden brown and nicely puffed up – you don’t want any soggy bottoms here. You can also make one large tarte by covering the frying pan filled with apples with pastry and baking.