First of all, peel the apples as neatly as possible, core, and cut into 8 pieces. Next, tip the sugar into a large pan and leave to caramelize on medium heat, add the butter and stir until melted. Carefully lay the apples in the pan, then cook in the sauce while occasionally stirring, until the apples start to soften. Pour and spread the apples and sauce into a tart pan and drape the pastry over the top. Remove the excess pastry and pierce with a fork a few times. Bake in a pre-heated oven to 180°C/356°F/gas 4 for 15 minutes, or until the pastry is crisp and golden brown. Remove from the oven and allow to cool for 10 minutes, then invert it carefully onto a serving dish. Serve the tart warm, with a spoonful of crčme fraîche and a fresh mint leaf.