Add the onion, red bell peppers, green bell peppers, garlic, and cilantro into a food processor or blender. Blend everything together until you have a chunky sofrito sauce.
Notes
If you’re using a high-powered blender like a Nutribullet, blend in short pulses until chunky.
You can use regular yellow onion or red onion. It doesn’t matter. We’re using mild onions for this recipe. I've used both for a sofrito recipe.
The bunch of cilantro was about 2 ounces.
Blend the sofrito in parts. I did about 5-6 batches due to the size of my blender.
Some sofrito recipes call for olive oil or salt. I don’t add those because I like to control those particular ingredients during the actual cook.