A calzone is basically a pizza, but folded over and then baked. It looks a bit like a Cornish pasty but it's made using bread dough and not pastry. You just knead together your bread flour, water and yeast with a little salt and sugar to make a regular bread dough. Leave it for its first proving for about 30 minutes. While the yeast is getting to work with that, you basically chop up all sorts of different vegetables and put them in a pan with some olive oil.
I used pitted olives, courgettes, aubergines, spianch, garlic and a couple of tins of tomatoes with some herbs. You could really add anything you like - mushrooms, cooked meat, pepperoni even. Cook until soft and a bit jammy, and then put to one side. When it's cooled down, you can tear in a couple of balls of mozzarella.
Once your bread's risen, tear off little blobs just slightly smaller than a tennis ball and roll out in a circle until they are about half a centimetre thick. Then dollop a couple of spoonfuls of the cooled filling onto one half of the dough circle. Make sure everyone gets some cheese. Press or fold the edges over to make a pasty shape and lay them on a floured baking tray (I use greaseproof paper). Leave them for 5 minutes or so until your oven is preheated (200C).
Bake for about 15 minutes - you can slash the tops if you like, so some of the sauce comes out and colours the top. Once they're golden, the bread is cooked and the veggies are hot all the way through, they are ready. They will also be volcanically hot. Leave to cool slightly before tucking in. We used these for lunchboxes and quick snacks. They're good cold, but I prefer them hot. Heat cooled ones in a hot oven for about 10 minutes.
There's a great recipe for calzone in Jamie Oliver's book Happy Days with the Naked Chef and also another one online here. I don't think it matters too much what you fill your calzone with, just think of anything you'd stick on a pizza and go for it!