Peel, halve, and core the apples.

Melt the butter in a 10” (25cm) oven-proof skillet over medium heat. A cast iron skillet or stainless steel skillet will work great. Add vanilla extract and salt, and mix.

Sprinkle the sugar on top of the melted butter in an even layer and arrange apple halves cut-side up on top of the sugar. Cook them over medium-low heat for 20-30 minutes or until the bottoms are soft and the syrup is caramel-like. The tops of the apples will be still undercooked.

Preheat the oven to 200C (395F).

Roll out the puff pastry on a lightly floured surface and cut out an 11” (28cm) circle.

Remove the skillet from the heat and place the dough circle over the apples. Tuck the edges down with a spatula and bake for 25-30 minutes in the middle of the oven, or until the crust is golden brown and the apples are fully baked.

Remove the tart from the oven and let it cool down until just warm to the touch. After, cover the skillet with a large serving plate and flip it. Lift the skillet to release the tart, sprinkle it with sea salt flakes, or serve it with a scoop of vanilla ice cream.