Instructions:

1. Peel and roughly chop the onion, carrot, and celery.
   
2. Heat a little sunflower oil in a large pan over medium heat. Add the chopped vegetables and sauté for 10 minutes, stirring frequently.
   
3. Stir in the tomato purée and half a cup of water. Mix well and bring to a boil. Then reduce the heat to low, cover, and simmer for about 30 minutes, or until the vegetables are soft. Stir occasionally and add a splash of water if needed to prevent sticking.
   
4. Once the vegetables are cooked, add finely chopped parsley, salt, ground black pepper, and a pinch of turmeric for a golden color. Mix well and cook over medium heat, stirring occasionally, until most of the liquid has evaporated.
   
5. Let the vegetable mixture cool, then blend it into a smooth purée using a blender or food processor. Weigh the purée (this will be your stock concentrate) to calculate the portion size. For example, if the ingredients for 6 L of broth yield 600 g of concentrate, use 600÷6=100 g of concentrate per liter of water to prepare the broth.
   
6. Spoon the concentrate into ice cube trays and freeze until solid. Once frozen, you can transfer the cubes to a freezer-safe bag or container for storage.
   
7. To prepare broth, add the frozen cubes to a pot of water, bring to a boil, and stir until dissolved. Adjust salt to taste.