Preheat an oven to 220 degrees fan/gas 9. Lightly grease a six-hole muffin tray. Roll out the puff pastry to a thickness of two millimetres and stamp out six circles of pastry (each 10cm wide).

Gently press the pastry circles into the hollows, to the top edge of each (so they can hold all the liquid), then refrigerate them.

In a mixing bowl, use a wooden spoon to beat the egg yolks with the sugar until smooth and pale, then stir in the flour.

In a small saucepan, heat the milk with the vanilla and orange zest until just before it starts to boil, then remove it from the heat. Gradually pour the hot milk into the egg mix, whisking all the time with a hand whisk, while not creating too much foam.

Just before baking, peel and core the apple and cut into dice-sized cubes. Place three to four cubes of apple in each pastry hollow.

Fill with custard to the top. Cook for 20-25 minutes, until puffed up, set in the middle and slightly browned on top. Serve warm with ice-cream or freshly whipped cream.