Prepare the salsa verde by blending the tomatillos, jalapeños, ¼ white onion, garlic, cilantro, chicken bouillon, and cumin with the ½ cup of tomatillo water.
Season the beef sirloin with salt and pepper.
In a skillet, cook the beef sirloin in avocado oil until browned on all sides.
Add the diced potatoes and the prepared salsa verde to the skillet.
Simmer the carne con papas en salsa verde until the potatoes are tender and the beef is cooked through.
Serve the dish garnished with the sliced white onion.
