Spray a frying pan with low calorie cooking spray and heat till hot. Throw in the onions and cook until soft. Add in the garlic and herbs and cook for a couple of minutes till the herbs become aromatic
Add in the carrot and celery, and cook for a further 5 minutes. Make sure to keep stirring
Add in the stock cube, balsamic vinegar and tin of tomatoes, then fill half of the tin with water and add that also. When the pan starts to bubble turn the heat down to medium and cook for 15-20 minutes - a good time to start slicing your vegetables!
Once cooked, attack with a stick blender/put into a food processor and whizz up until smooth. Pour into a large oven proof dish
Once finished sprinkle a liberal amount of salt and freshly ground black pepper on top. A few sprays of low calorie cooking spray and top with a piece of baking parchment/greaseproof paper. This is just to stop the wafer thin slices from catching in the the hot oven