2: Remove cores, no matter if the apples break during this operation.
3: Cut each half apple in half again.
4: Melt 30 g butter in a large pan or frying pan. Then sprinkle with 50 g caster sugar and put apples on top. Allow to caramelise on low heat.
5: Meanwhile, spread out the first circle of puff patry (this will be the pie base), prick it with a fork or a pique-vite. Put back in the fridge.
6: Spead out the second puff pastry circle (pie lid) and make a small hole in the centre to allow steam to escape during cooking (the "chimney"). Put back in the fridge.
7: Apples will be caramelized after about 30 minutes.
8: Take out the pie base, place on work surface and spread the apples over, caramel side upwards and packed well towards the centre, to within about 1 cm - ½ inch of edge.
9: With a brush, moisten edge of pastry with cold water.
15: Leave in the fridge while oven preheats to 210°C or 410°F. Put in the oven for about 25 minutes.
16: Watch the coloration: as soon as it looks like the photo, it's done.
17: Serve warm if possible.
Remarks
You might find it easier to glaze with beaten egg-yolk just after cutting the "chimney". If you prefer the classic version, with frangipane or almond cream, check out this other recipe: epiphany galette.