Prepare sauce before starting on sandwiches.

Toast peppers on a comal or griddle until fragrant, being careful not to scorch.

Allow to cool then snap off stems and shake out seeds.

Soak peppers in 2 cups hot water for about half an hour; drain and discard soaking water.

Place soaked chiles in a blender or food processor with one cup fresh water,garlic, ketchup, vinegar, olive oil, salt and cumin and puree until smooth.

Strain sauce through a mesh sieve if desired (for a smooth texture).

Peel potatoes and finely dice. Cook potatoes in a skillet with chorizo and onion until meat is done and potatoes are tender.

Drain off any excess grease.

Pick out some of the bread inside if you like. Dry that bread for bread crumbs to use later.

Dip rolls briefly in adobo sauce to coat.

Place meat filling inside roll and griddle (like a grilled cheese) until bread crisps.

Lift bun top and add lettuce, crema, cheese and pickled onions.