Begin by preparing your ingredients for the Salsa Roja. Dice four Roma tomatoes, half a white onion, and a couple of cloves of garlic. Rinse and chop a handful of fresh cilantro, and stem two serrano chiles.

Preheat a cast-iron skillet over medium heat. Once hot, add the whole Roma tomatoes and serrano chiles. Roast each side for about 5 minutes, turning occasionally until the skins are blackened and blistered.

Transfer the roasted tomatoes and chiles to a blender. Add the diced onion, garlic, and cilantro. Blend on high for 30 to 60 seconds until you reach your desired consistency.

If you prefer a deeper flavor, transfer the blended salsa to a saucepan. Add a splash of olive oil and bring to a gentle boil. Allow to simmer for about 15 minutes, stirring occasionally.

Once simmered, remove from heat and stir in a pinch of salt and freshly squeezed lime juice to taste.