This is such an easy recipe and it can be made a day or two ahead to save time. It's also a cheap meal if you need to save money or are working to a budget.
Depending on the type of cheese you use in the tart, you can make it as luxurious or simple as you wish. For this one, I chose cheddar. But, I've also been known to through in some pecorino or mozzarella.
For the tart:
The first thing to do is blind bake the pastry. This is done by greasing your tart dish, lining it with shortcrust pastry, placing greaseproof paper on top of the pastry and filling it with ceramic beans or dried beans. This is then placed into a hot oven for 10 minutes or until the pastry is cooked and lightly golden. The reason for this process is that if it is not done the pastry will not cook underneath its filling (I shall do a post at a later point for pastry).
Gently sweat 2 finely sliced onions in some butter for 10 minutes until soft and transparent. Allow to cool. In a bowl, mix 2 beaten whole eggs and 1 egg yolk, 300ml single cream and 150g cheese. Mix in the onions and season. Tip into the blind baked pastry in the tart dish and bake for 1 hour at Gas Mark 4. The mixture should be set but not brown too much on top. Leave to cool before turing out on to a plate.
For the new potatoes:
Cut any larger potatoes so that they are all roughly the same size. Boil in a pan of salted water, with a small handful of fresh mint, for 10-15 minutes (depending on size). Drain, return to the pan, season and add a knob of butter. Serve either hot or cold.