Boil potatoes in water with salt until soft. Drain potatoes. Smash potatoes until somewhat chunky. Mix in sour cream, butter, milk, salt and black pepper, until evenly mixed.
Warm tortillas in microwave for about 1 minute, or until softened. Put a tablespoon of potato mix into tortilla and fold in half. Then put in pan with hot oil (on medium heat) and fry until both sides are golden brown, careful not to burn.
Optional: You can also put leftover rice or Mexican soup (fideo).
Top with cheese, lettuce, salsa and radishes and enjoy!