1. First make the pastry by mixing the flour, salt and sugar together, then rub in the 175g butter and finally bring together with the water, making sure you add just what is needed. Allow the pastry to rest for 20 minutes and then roll out into a loose-bottomed tart tin and bake blind, then allow to cool.

2. Melt the butter in a medium saucepan, add the onions and season well with salt and pepper.

3. Cook the onions over a medium heat until they start to cook down and release their liquid, mixing as you go.

4. When the onions are soft, place a lid on the saucepan and turn the heat down. Continue to cook for at least 20 minutes until the mixture starts to resemble a jam.

5. Remove the lid and increase the heat to remove any liquid.

6. In the meantime, make the custard by beating the eggs and adding the cream. Season with salt, pepper and nutmeg.

7. When the onions are cool add to the custard and mix well. Pour into the baked tart case and bake in the preheated oven for roughly 15 to 20 minutes or until set.