01 -
Preheat the oven to 170°C (150°C fan) or gas mark 3.
02 -
Place the halved tomatoes, sliced onions, sliced garlic, and fresh herbs in a roasting tin. Season with salt, black pepper, and brown sugar if using.
03 -
Drizzle balsamic vinegar and olive oil over the vegetables. Stir thoroughly or use hands to ensure even coating.
04 -
Place the roasting tin on the centre rack and roast until onions are soft, tomatoes have broken down, and contents are caramelized. Stir occasionally and lower the temperature if vegetables begin to darken too quickly. Roasting time varies: cherry tomatoes require 20–30 minutes, larger tomatoes up to 1 hour.
05 -
Remove any tough herb stems, then transfer the vegetables and all roasting juices to a blender or a deep bowl for a stick blender. Blend to desired consistency.
06 -
For a very smooth texture, pass the blended mixture through a fine sieve to remove seeds and large pieces of skin.