1) Preheat oven to 190 celcius
2) Peel, core and quarter pears
3) Combine sugar and lemon juice in a jug and stir until combined
4) Pour into a heat proof pie dish over low heat
5) Stir for 5 minutes until sugar dissolves
6) Increase heat slightly to medium and cook until sugar starts to bubble and caramelise. This takes approximately 5 minutes. Keep stirring and breaking up the bubbles.
7) Arrange the pear slices on the pan. Dot the pears with butter and scatter with thyme leaves. Cook for 5 minutes until the pears are slightly cooked.
8) Let cool to room temperature.
9) Cover the caramelised pear with a sheet of puff pastry. Tuck any excess under the pears.
10) Cook in the oven for 30-40 minutes or until the pastry turns golden brown.
11) Remove from the oven.
12) Invert the tart only just before serving to avoid pastry from softening. If you're not serving straight away, reheat in the oven still upside down, at 100 degrees Celcius and turn it over just before serving to keep the pastry nice and crisp. I've made the mistake of turning it over and then reheating it only to find the pastry underneath soft and gluggy. We all learn from our mistakes!
13) Garnish with sprigs of fresh rosemary.
14) Serve with cream, vanilla ice cream or plain yoghurt.