Caramelised onion and sweet potato tart

You know when you have to 'bring a plate' to your last antenatal class and you forgot about it until that day and you have spent your weekly budget, and you're not sure what to do? But then you discover that you have an onion, and a sweet potato, and a little bit of left over mozzarella and parmesan from the weekend's lasagne. And there's some puff pastry in the freezer. And it's the depths of winter and you're supposed to be writing your thesis and you can think of nothing better than having an excuse to put the oven on?

Well, I'm sure we've all been there. Or at least somewhere entirely dissimilar to there. Fortunately, this tart is the solution to all manner of crises. It's pauper ingredients gussied up as fancy French business. It's pretty easy. And it's really scrummy. It would work with all different kinds of cheese, and using this template I'm pretty sure you could do good work with potatoes, mushrooms, and all manner of other seasonal veg.

Ingredients:

• 1/2 a large sweet potato
• 1 brown onion
• 1 clove garlic
• 50 grams butter
• splash of sherry vinegar 
• 2 teaspoons brown sugar
• 1 big handful of grated mozzarella
• 1 tablespoon grated parmesan
• 2 sheets frozen puff pastry
• salt and pepper to season

Finely slice your onions, the thinner the better. Heat the butter in a large frying pan on a medium heat, and add the onions. Soften then for about 10 minutes until they are golden and then add the splash of vinegar and brown sugar and continue to sweat the onions for another 5 minutes.

While the onions are cooking, finely slice your sweet potato, then add it to the pan. Sautee the potato for about five minutes until it starts to soften. Add salt and pepper to taste.

Grate the cheese and toss half of it through the mixture, reserving half for the top.

Take your two sheets of puff pastry which should be properly thawed by now. Because this is Australia puff pastry only seems to come in squares, which is the wrong shape and thickness for this tart. So scrunch them into a ball, and roll them out again into a vaguely circular shape about 2 millimeters thick. Don't worry about it being neat, you can pass any wonkiness of as 'rustic'.

Tip the onions and sweet potato mixture into the centre, leaving a 2 cm border. Fold the pastry border in and sprinkle the remaining cheese over the top. Brush the pastry edges with a little milk and cook in a hot oven (220 C) for about 18 minutes.

When you remove the tart from the oven it will have puffed up into a glorious golden pouffie thing. Let it cool for a few minutes before slicing it. Da na!