1. Wash the tomatoes and chop the carrots, celery and the onion.
2. Put everything in the pot along with a finger level of cold water.
3. Let it simmer and cook for 25 minutes or until the carrots is soft.
4. Put part of the ingredients in the grinder or sifter and grind till you get a smooth pulp.
5. Continue grinding until all the ingredients are over, discard any skin of big chunks that you may get while grinding the tomatoes.
6. Serve it with your pasta or lasagna or simply store for later use.