Add the whole tomatoes, onion, serrano and garlic to the skillet, and toast until charred on each side, about 2 minutes per side.
6 roma tomatoes, 1 small white onion, 1 serrano pepper, 3 cloves garlic
Transfer to a cutting board to cool (the garlic might char before the others, so keep an eye on it). Be sure to open a window or turn on your overhead fan, as the skillet will likely smoke as you char the ingredients. Once cool, coarsely chop the tomatoes and onion. Remove the stems, seeds, and ribs from the serrano (leave the seeds and ribs intact for a spicier salsa), and peel the skin from the garlic.
Add the garlic, onion, peppers, and tomatoes to a food processor. Pulse until well-blended but still very chunky, about 6 pulses. Add the cilantro and pulse until uniform but still a bit chunky, about 6 more pulses.
2 tbsp cilantro
Warm the lard in a large saucepan over medium heat. Add the salsa and bring to a simmer; reduce heat to medium-low and simmer until slightly darkened, about 10 minutes, stirring often. Season with salt to taste, then remove from heat and serve warm or at room temperature, with tortilla chips.