Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.

Roll out the thawed puff pastry slightly to smooth the seams, then score a 1-inch border around the edge with a knife (do not cut all the way through) to create a crust rim.

In a medium bowl, cream together the softened butter and sugar until smooth, then beat in the egg and vanilla extract.

Stir in the almond flour and ground walnuts until a thick, spreadable paste forms (this is your walnut frangipane).

Spread the frangipane mixture evenly inside the scored border of the pastry.

Arrange the apple slices over the frangipane in an overlapping shingle pattern.

Bake for 35-40 minutes, until the pastry is puffed and golden brown and the apples are tender.

If using apricot preserves, microwave them with a teaspoon of water for 15 seconds and brush over the hot apples for shine.

Allow the tart to cool for at least 10 minutes, then generously drizzle the salted caramel sauce over the top before serving.