Place the fresh tomatoes, onion, garlic, peppers, cilantro, lime juice, 2 teaspoons cumin, 2 teaspoons sugar (if using), and salt in a food processor. Pulse until the contents are fine and well blended.: When you begin pulsing, listen for the rhythmic chopping sound that tells you the blades are doing even work. You will smell a bright citrus note from the lime and a warm, nutty scent from the cumin that mingles quickly with the sharpness of raw onion and the grassy, almost soapy lift of fresh cilantro . Aim for a consistency that is finely chopped but not completely liquified unless you prefer a smooth salsa. This creates body and texture so chips can grip the bits. A common mistake is over pulsing until everything is a puree, which can flatten the perception of fresh ingredients, so pulse in short bursts and scrape down the sides if large chunks remain.
Pour in the crushed tomatoes and green chiles. Puree until mostly smooth. Taste, then add more cumin and sugar if desired. Refrigerate until ready to serve.: As you add the canned crushed San Marzano tomatoes and diced green chiles , the mixture will loosen and the aroma will shift toward a deeper tomato sweetness and subtle roasted notes from the can. Puree just until mostly smooth, leaving a bit of texture so the salsa feels lively on the tongue. Watch the color become more uniform and the sound of the processor deepen into a steady whir, which indicates things are blending properly. Over blending here can make the salsa watery and lose its fresh bite, so stop when you still see tiny flecks of herbs and pepper.
Taste, then add more cumin and sugar if desired.: Once blended, spoon a small sample and pay attention to the balance of acid, heat, salt, and sweetness. The immediate tang of lime should be present, but the warmth of cumin may need a gentle boost to round the profile, or a pinch of sugar can tame sharp acidity if the tomatoes are very tart. Make adjustments conservatively, mixing after each small addition and tasting again. A frequent error is to add too much of any one seasoning at once, which can be difficult to correct, so increment slowly.
Refrigerate until ready to serve.: Chilling helps the flavors marry and settle, producing a more cohesive salsa. Place the finished salsa in an airtight container and refrigerate for at least a short rest, though I often let it rest for a few hours if time allows. The cold will slightly mute raw edges and let the cilantro and spices integrate. Avoid leaving the salsa out at room temperature for extended periods, as it is fresh and perishable; refrigerate promptly to preserve brightness and food safety.