Peel and chop the potatoes into 1-inch cubes. Add them to a large pot, cover with cold water, and bring to a boil. Reduce the heat and simmer for 15 minutes until tender.
While the potatoes are cooking, heat a large skillet over medium heat. Add the ground beef and break into small pieces. Cook until no longer pink.
Add the onions and minced garlic. Cook until the onions are translucent and almost all the water is evaporated, about 5 minutes, you should be able to hear the oil sizzling.
Add salt, cumin, and black pepper. Cook for 1 minute. Remove from the heat and stir in the butter. Set aside.
Drain the water from the potatoes and gently mash them. Be careful not to overmash them or they will become gummy.
Add the potatoes to the beef and stir until JUST combined.
In a shallow dish, combine the eggs, flour, and salt. Whisk until smooth.
In another shallow dish, pour in the breadcrumbs.
Grab a ball of potatoes and shape into a disc. Dip it in egg wash then coat it in breadcrumbs. Deep-fry at 350°F for 2-3 minutes on each side, or spray with oil and air-fry at 400°F for 15 minutes, flipping once.