Preheat the oven to 200C/400F (180C/355F fan). Place the tomatoes in a large roasting tin along with the garlic bulb halves to the tin, skin side down.
Pour on the oil, season and roast for 45 minutes, giving the tray a shake half way so that they cook evenly.
Remove from the oven and squeeze the garlic flesh back into the pot, discarding the skins.
Add the boiling water, stock cube and all the tomatoes and blend until smooth.
Pour into bowls. Serve with a blob of crème fraîche.