This balsamic roasted tomatoes and onion is one of my favourite or "staple"side dishes because it's so easy to make and it goes well with most roasts and grilled meat or fish (I cook it on the lower shelf in the oven whilst the main dish is roasting on the top).You can add a spoonful of brown sugar if you'd like it more caramelised - I think the balsamic vinegar is enough though. Also, depending on your main dish, you can use other herbs such as tarragon, thyme, rosemary, basil etc. Any leftovers make a nice salad-base, pizza-topping or are perfect for puff-pastry tartlets and party nibbles (particularly combined with blue cheeses).