First, unroll the puff pastry. Sprinkle the grated cheddar cheese over one half, leaving a 2cm border around the edge. Fold over and press down the edges to seal.
Take a rolling pin and gently roll the pastry so it begins to flatten. Fold it in half, then in half again, wrap in clingfilm and pop in the fridge to firm up, approx. 30 minutes.
Meanwhile, take the pan you will use (8-10inch recommended, I used 9inch) for your tatin, and put on a medium heat. Add a drizzle of olive oil, and then the halved beetroots and thyme and sauté for 4-5 minutes.
Add the honey, balsamic vinegar and some salt and pepper. Once bubbling, simmer rapidly over a high heat until the liquid has reduced right down and become a thick, sticky glaze; there should only be a small amount of liquid left or you will end up with a soggy tatin.
Allow to cool then arrange the beetroots so that they are all rounded side down.
Preheat your oven to 190C/375F/gas mark 5. Roll out the pastry again, so it’s back to its original size; then cut out a circle slightly larger than the size of the pan.
Lay the sheet of pastry over the top of the beetroot in the pan and tuck in the edges. Bake for about 25 minutes until the pastry is golden brown and the filling is bubbling.
Allow the cooked tart to sit in the pan as it is for 20 minutes, then place a plate on top of the pan and carefully flip it over, allowing the tart to come out onto the plate.
Top with the goats cheese and serve straight away with a watercress salad.