Heat oven to 200C/180C fan/gas 6. Cut a round of pastry the same size as the ovenproof pan you are using, then put it on a baking sheet. Leave to chill in the fridge for at least 30 mins.

Heat the oil, butter and thyme in the pan until the butter has melted. Add the sugar and stir in. Put the onions and chicory cut-side down in the tin. Season and allow to caramelise for about 10 mins. Squeeze over the lemon juice, then remove from the heat and leave to cool slightly.

Put the disc of pastry on top and push it down around the edges of the pan, so it’s encasing the contents. Pierce the pastry with a knife all over to let out the steam, then bake in the oven for 40 mins, or until the pastry is puffed and golden. Allow to cool for 10 mins before carefully turning out onto a plate. Don’t panic if it sticks to the pan – you can gently scrape the pieces off using a palette knife, then set them back in the tart. Season. Tear the cheese over the top, scatter over the hazelnuts, if using, then drizzle with a little more olive oil to serve.