Preheat the oven to 350°F.
Spread the softened butter evenly across the bottom of a 9-inch pie dish.
Sprinkle the brown sugar over the butter, followed by the cinnamon and a pinch of salt.
Core the apples and slice them about ¼ inch thick.
Gently toss the apple slices with the vanilla extract and lemon juice, then arrange them in overlapping layers over the brown sugar mixture.
Avoid overcrowding the apples to prevent excess moisture.
Place the puff pastry over the apples, tucking the edges gently around the fruit.
Prick the pastry a few times with a fork to allow steam to escape.
Bake for 35–45 minutes, or until the pastry is golden brown, fully cooked, and the apples are tender.
If needed, bake a little longer to ensure the pastry is crisp.
Let rest for about 5 minutes, then carefully place a large serving plate over the dish and flip the tart upside down, being careful of the hot caramel.
Serve warm with vanilla ice cream or whipped cream.
