Directions:

1. Preheat oven to 175ºC.

2. Peel onions and cut into thick rounds. Pour enough olive oil into an ovenproof frying pan to thinly coat the base and heat over medium-high heat. Add onions to the pan and season with a pinch of salt and pepper. Reduce heat to low and cook for 5 minutes, then flip onions and cook for a further 5 minutes.

3. Arrange onions in an even layer in the pan. Mix sugar and balsamic vinegar together and pour over the onions, then remove from heat.

4. Cut pastry into a circle to fit the pan, allowing a little overhang. Place pastry on top of the onions, ensuring that they are completely covered and tuck excess pastry into the sides of the pan. Use a fork to poke a few holes in the pastry and place in the oven to cook for 20 to 25 minutes or until the pastry is golden brown.

5. Remove from oven and allow to sit for 5 to 10 minutes, then place a serving plate over the frying pan and quickly flip so that the onions are on top.

6. Garnish with thyme sprigs and serve.