Heat water in a kettle or in a pan on the stove. Meanwhile, snip the tops off the chiles and remove the seeds.

Toast the guajillo chiles over a hot pan for 10 to 15 seconds, turning constantly to ensure they do not burn. Move the toasted chiles to a bowl and pour the hot water over them. Let them soak for 10 minutes until the chiles are soft.

Add only the chiles to a blender along with the garlic cloves and chicken broth. Blend until completely smooth. Set a metal strainer over a bowl and strain the sauce to remove any seeds or leftover chile skin scraps.

Taste it, and stir in salt if needed. Transfer to an airtight container. It can be stored in the fridge for a few weeks.

Heat a cast-iron pan over medium heat. Add the chorizo so that the fat from the sausage starts to render out, about 2-3 minutes.

Chop the potato into small dice and add it to the chorizo. Sauté the chorizo and potato for another 8 minutes until the potatoes just start to brown and have softened.

Note: You can parboil the potatoes after dicing them so they cook faster in the pan.

Meanwhile, spoon the guajillo chile sauce onto a plate and dip the bread roll to completely cover the outside of both halves. Add a drizzle of neutral oil to a pan and heat it over high heat.

Once the pan is hot, add the dipped bread halves to the pan and sear both sides. Flatten the bread halves a bit with a spatula. Once they are toasted on both sides, turn off the heat.

When the chorizo filling is done, turn off the heat and add it to one-half of the bread.

Assemble the sandwich by adding one or two spoonfuls of cotija cheese, salsa, shredded lettuce, and pickled onions. Then slice and enjoy.