1 Preheat your oven to 180 degrees Celsius. Cook the onions in the butter over a medium heat for 20 minutes until they are soft and golden brown, then add the sherry and allow it to be absorbed.

2 Drain the raisins, add them to the onions along with the thyme, then season with salt and pepper.

3 Roll the pastry out a little on a lightly floured surface.

4 Oil and flour a 25cm loose bottomed tart tin.

5 Line the tin as best you can making sure you have a slight overhang around the edge of the tin. This will prevent shrinkage later.

6 You may have to take some excess pastry to patch up any shortcomings; simply trim some off one side and press it into the less abundant side.

7 Prick the base lightly with a fork and place into the fridge to rest for 15 minutes.

8 Line the tart base with parchment paper and fill the base with ceramic baking beans or a good amount of rice.

9 Bake in the oven for 20 minutes before removing the baking beans and parchment.

10 Return to the oven for 10 more minutes, until golden and crisp.

11 Spread the caramelised onion mixture over the base of the tart.

12 Whisk the eggs with the milk, cream, nutmeg, salt and pepper, then ladle this over the top of the onions.

13 Sprinkle the cheese over the custard mixture, then put back in the oven at 170 degrees for 25-30 minutes, until golden and the custard has a slight wobble in the centre.

14 Allow to cool for at least 10 minutes.

15 Trim the excess pastry, then carefully remove from the tin and slice.