Prepare the shortcrust pastry: Quickly mix all the ingredients together so the butter doesn’t melt.
Prepare the apples: Peel the apples, quarter them, and remove the cores.
Assemble the cake: Place small pieces of butter and half of the sugar in the bottom of your cake pan. Layer half of the apple slices with the rounded side facing up, sprinkle with the remaining sugar, and then top with the rest of the apple slices, this time with the rounded side facing down.
Bake the apples: Preheat your oven to 200–220°C (400°F). Bake the apples for about 10 minutes on the lowest rack.
Prepare the pastry: While the apples are baking, roll out the pastry until it's about 2–3 cm thick and slightly larger than your cake pan.
Cover the apples: Once the apples have baked for 10 minutes, take the pan out of the oven and cover the apples with the pastry. Seal the edges and prick the pastry with a fork to let the steam escape.
Bake the tart: Lower the oven temperature to 180°C (350°F) and bake for another 25–30 minutes, or until the pastry is golden brown.
Flip the tart: Let the tart cool for 5 minutes, then carefully flip it onto a serving plate.
Caramelize the apples (if needed): If the apples aren’t caramelized enough, put the tart on the top rack of the oven at 200°C (400°F) for 5 more minutes. Watch carefully so it doesn’t burn.
Serve: Enjoy your Tarte Tatin warm, with a scoop of vanilla ice cream or a drizzle of custard. Simple and delicious!