This classic molcajete recipe comes from famed Latin chef Richard Sandoval, and despite it being a chef recipe, it's easy. Using store-bought tomato salsa as a base, it uses fresh tomatoes and spicy serrano peppers to make it fresh and bright.
On a grill or in a pan over high heat, roast the tomato until charred. Set aside and let cool. Roast the serrano pepper until charred and remove from heat. When tomato has cooled, finely dice and divide. Remove the stem from the serrano pepper and finely dice. Blend 1/2 of the chopped tomato with the serrano pepper to make a paste.Oil the green onions and lightly sauté until browned and cook through, then finely dice.
In a bowl of a food processor, add the salsa, other 1/2 of the chopped tomato, serrano paste, salt, and pepper and process until smooth. Mix in the green onions, diced onion, and cilantro and process for another 30 seconds. Let cool, cover, and refrigerate until ready to serve.