Fill a large pot or Dutch oven with water and bring it to a boil over high heat. Add the potatoes and boil for 20 to 25 minutes, or until they are fork tender. Drain the potatoes and transfer them to a large bowl.
Melt the butter in the pot used for cooking the potatoes over medium-high heat. Add the garlic and cook for 30 seconds, or until fragrant.
Add the potatoes, cumin, chili powder, and salt and mash the potatoes until they are creamy and smooth. Taste and season with more salt as needed. Set aside.
In a large skillet, heat the oil over medium-high heat.
Spread about ¼ cup of the mashed potatoes on one side of the tortillas and fold them to create tacos.
Fry each taco for about 2 minutes per side, or until the tortillas are golden and crispy, flipping the taco carefully with a small spatula.
Place the tacos on a plate or baking sheet covered with paper towels to soak up any excess oil. Continue frying the tacos in batches until complete.
Stuff or top the tacos with shredded lettuce, cotija cheese, Mexican crema, and your favorite hot sauce.
Notes
The potato filling can be made up to 3 days ahead of time and stored in an airtight container in the refrigerator until ready to use.
Warm up the corn tortillas before assembling the tacos to prevent them from cracking.
To keep the tacos warm while you finish frying all of them, you can place them on a large baking sheet in a 200°F oven.