Step 1

Preheat the oven to 400°F. Line a baking sheet with parchment paper or a silicone mat.

Step 2

In a bowl, combine the apple slices with the brown sugar and lemon juice. Set aside.

Step 3

In a large bowl, beat the butter and sugar together with a spatula until combined and fluffy. Add the egg and mix in well.

Step 4

Add in the almond meal and the splash of cognac (or rum) and stir together until combined well. Temporarily set aside.

Step 5

Unfold your sheet of puff pastry and place a round plate that’s about 8 inches in diameter, face down, on top of the pastry. Trace the rim of the plate with a knife then run the knife along the tracing again to completely cut out the pastry round. Repeat this step with the second sheet of puff pastry, except this time, trace around the rim of the plate, leaving 1/2 an inch space between where you actually cut and the plate. You want this second round to be slightly larger than the first one.

Step 6

Place the first pastry round on your prepared baking sheet. Spread half of the frangipane filling over the pastry, leaving a 1/2 inch border bare along the rim of the pastry round. Place the marinated apple slices on top, then top with the rest of the frangipane, smoothing the frangipane out as carefully and best as you can.

Step 7

Place the second pastry round on top, pinching the edges together to seal the pastry envelope. Flute the edges, if you desire, and then use a sharp knife to make diagonal (zig zag) cuts on the surface of the pastry. Alternatively, you can make radial cuts to create swirls.

Step 8

Beat the extra egg before brushing it on top of the pastry. Bake the cake for 20 to 30 minutes, until the pastry is golden and crisp on top and up the sides (some ovens get hotter, which is why you'll want to start checking the pastry at the 20 minute mark for readiness).