Add the tomatoes, half of the onion, garlic, jalapeño, and 1 cup of water to a blender. Blend until smooth and set aside.
Pat the beef dry with paper towels. Season it with salt and black pepper.
Heat the oil in a large Dutch oven over medium-high heat.
Working in batches if necessary, add the beef in a single layer. Brown it for about 2 to 3 minutes per side. Don't crowd the pot. Transfer the browned beef to a plate.
Reduce the heat to medium. Pour the blended tomato mixture carefully into the same pot, scraping up the browned bits from the bottom.
Cook the tomato sauce for about 5 minutes, stirring occasionally, until it darkens slightly and begins to concentrate.
Return the beef and any accumulated juices to the pot.
Add the beef broth, cumin, and Mexican oregano. Stir well and bring everything to a gentle boil.
Reduce the heat to low, cover, and simmer for about 50 to 60 minutes, or until the beef is beginning to become tender.
Add the potatoes and stir them into the sauce. If the mixture looks too dry, add a splash more broth.
Cover again and simmer for another 25 to 30 minutes, until the potatoes are fork-tender and the beef can easily be cut with a fork.
Remove the lid for the final 5 to 10 minutes if you'd like a thicker sauce.
Taste and adjust the salt.
Spoon into bowls or onto plates and serve hot with warm corn tortillas. Finish with cilantro if you like.