1. Peel the potatoes and cut into roughly 1-inch cubes. Place in a medium pot with water, two teaspoons of salt and cover.
2. Bring to a boil, then simmer for about 12-16 minutes or until the potatoes are tender.
3. Drain the potatoes and return them to the pot.

Assembly

1. Add the butter, additional 2  teaspoons of salt, fajita taco spice and queso fresco to the cooked potatoes. 
2. Using a potato masher, mash the mixture until smooth.
3. Warm the tortillas one at a time on both sides in a dry 12-inch frying pan. 
4. While the tortilla is warm, spread about a quarter cup of potato into each tortilla.
5. Place a thin slice of thinly sliced tomato and gently fold in half to form a taco.
6. When all tacos are assembled, heat the oil in the same frying pan until hot and shimmering.
7. Fry each taco on one side until crisp, about a minute and half, then flip with tongs and repeat. You can fit 3 in the pan at a time.
8. Drain tacos on a paper towel and sprinkle with a little additional salt if you like.
9. To serve, add sour cream, guacamole, or your favorite salsa.