Add potatoes to a pot and cover with at least two inches of salted water. Bring to a boil and cook for 20-25 minutes, until tender. Drain and let cool. Peel and cut into 1-inch cubes. Set aside
While your potatoes are cooking, preheat your oven to 350 degrees. Stem, seed, and devein the chiles. Place the chiles on a cookie sheet and toast for 5 minutes.
Move to a pot along with the garlic and the roughly chopped half of the diced onion. Add enough water to cover, bring to a boil, then cover and reduce heat to a simmer for 15 minutes.
Remove the chiles, garlic, and onion with a slotted spoon and place in a blender jar with one cup of tap water and 1 teaspoon of salt. Blend until very smooth. Press through a fine-mesh sieve with the back of a wooden spoon until most of the liquid has passed through.
Cook the finely dice half of the onion and all of the jalapeno in a skillet over medium-high heat for 5 minutes.
Add the chorizo and cook over medium-high heat until done. About 5 more minutes. Add the potatoes, very lightly mash them (Not mashed potatoes, just slightly crushed. You want chunks), and mix them in. Cook for an additional 2-3 minutes.
Cut the telera/bolillos in half, brush the cut side with butter and toast, cut side up, under your broiler until lightly browned. Remove from the oven and, using a silicon pastry brush, thoroughly coat the outside (not the cut side) of the bun with the chile mixture.
Add 2-3 tbs. of vegetable oil to a cast-iron skillet and preheat over medium-high heat, then place the bolillos in the skillet cut side up (the sauced outside should be down in the pan), and fry until the outsides get hot and slightly crispy. About 2-3 minutes.
To assemble, add potato/chorizo mixture, the crumbled queso fresco, a good drizzle of crema, and top with some shredded lettuce.
Slice the sandwiches in half and serve with pickled jalapenos, cold beer, and lots of napkins.