Oh, rarely has a dish been so badly abused than the Tarte Tatin. Common mistakes are: too little caramelisation and too few apples, with a pale, flabby puff pastry layer. The apples should be halved and packed, upright, into the buttery caramel base, and the pastry should be cooked until crisp and flaky, to provide contrasting textures. I was privileged, many years ago, to watch a live cookery demonstration by the demi-God, Raymond Blanc. From what I can remember, dragged out of memories obscured by sheer lust and awe, he produced a Tatin of utter brilliance (I also remember him tasting olive oil by pouring it onto his palm and licking it off - I didn't recover from that for several weeks). So, I have followed his recipe every Autumn for our annual treat, probably for the last 20 years or more. The recipe works, so I shall simply point you to it to follow too, along with a picture from his cookbook that shows what perfection should look like.