To make the shortcrust pastry, combine the flour, salt, oil, and butter in a food processor and pulse until lumps form.
Add the ice-cold water and mix again until the dough resembles coarse sand.
Shape it into a disc, wrap in plastic, and refrigerate for at least 30 minutes.
Once chilled, roll out and press the dough into a 9-inch tart pan.
Preheat your oven to 200°C (375°F).
Peel, core, and slice the apples, then arrange them neatly over the pastry base.
In a bowl, whisk together flour, eggs, 1/3 cup sugar, and crème fraîche until smooth, using a hand mixer if available.
Pour this custard over the apples.
Mix the remaining sugar with cinnamon and sprinkle over the top.
Bake in the center of the oven for 40–45 minutes until golden.
Let the flan cool for at least 15 minutes, then transfer to a serving plate.
Sprinkle with extra cinnamon sugar if desired, and serve.