Peel, core, and slice the Granny Smith apples.

In a bowl, combine the sliced apples, slivered almonds, ground almonds, egg, and caster sugar.

Mix the filling ingredients until well combined.

Cut each sheet of puff pastry into two equal rectangles (approximately 30cm x 15cm).

Place one pastry rectangle onto a greased baking tray.

Place a line of the apple and almond filling down the center lengthwise of the pastry.

Brush the edges of the pastry with beaten egg.

Lay the second sheet of pastry on top of the filling and the first sheet, pressing lightly to seal the edges.

Gently flatten the top of the pastry with your hand.

Repeat the apple/pastry layering process if you want to add a second layer, finishing with a layer of puff pastry on top.

Glaze the top pastry layer with beaten egg.

Sprinkle the top with extra slivered almonds and caster sugar.

Bake in a preheated oven at 190°C (380°F) for approximately 25 minutes, or until the pastry is golden brown and crisp.

Remove from the oven and let cool slightly.

Serve warm with cream or ice cream.