Place garlic and onion in the bowl of a food processor fitted with a steel blade and process to a paste.
Add remaining ingredients and process until mixed and relatively smooth. You may work in batches as necessary, and consider pulse-processing this salsa so that you have more control over the consistency of the end product.
Pour the processed salsa into a large heavy-bottomed pot and bring to a boil. Reduce to simmer and cook for 15 to 20 minutes or until the mixture has thickened slightly. Remove from the heat and set aside to cool.
This Salsa is best served either slightly chilled or at room temperature. You can store it, preferably in glass containers, sealed and refrigerated for up to weeks.
Note that this salsa tastes even better the longer it’s allowed to sit.