By Victoria Alexander and Genevieve Harris
We use Rough Puff Pastry to make this tart. You can use readymade puff pastry or shortcrust pastry if you prefer. Any strong—flavoured blue cheese can be used, such as Norzola or Roquefort. You will need eight individual tart tins with removable bases, 10 cm (4 in) diameter and 1.2 cm (½ in) deep.
TO CARAMELISE ONIONS, peel the onions and slice them very thinly. Heat the oil in a medium-sized saucepan over a low heat. Add the onions and cook slowly until they are a deep golden brown and very soft, about 30 minutes. Drain off any remaining oil and set the onions aside.
TO MAKE TART FILLING, in a bowl, mix together the blue cheese, mascarpone and egg yolk.