I know that its easier to simply go to the store and buy paste, but trust me, homemade is so much better. It takes a lot of time and work, but it can be done.
4 Quarts Roma Tomatoes, peeled and chopped
3/4 C Red Bell Pepper, cut into small pieces
1 Bay Leaf
Combine all ingredients in saucepan over medium heat. Allow to cook for about 1 hour. Strain mixture through mesh sieve. Return liquid to saucepan and cook over low heat for about 2-3 hours or until thick. Store in airtight container in refrigerator until ready to use.