Run your purple potatoes under your faucet to remove any excess dirt. Then dry.
Cut the potatoes into equal sized cubes. You don't need to peel them.
Add cooking oil to your cast iron skillet. Heat up the skillet over medium high heat.
When the skillet is hot, add your potatoes. Add in all of your seasonings.
Cook for 20 to 25 minutes, stirring every 5 mins or so to evenly brown your potatoes. If they are getting too dark before being done in the middle turn down your heat.
Notes
If you want to use onions, add them and cook them for 5 minutes before adding the potatoes. For fresh garlic, just add that at the same time as the potatoes. You might want to lower your heat a little so you don't burn the garlic. To make it a breakfast skilletCook bacon or sausage in the skillet before the purple potatoes.When the meat is done remove from the skillet. Add more oil if there isn't enough in the skillet and then cook the potatoes as instructed above.When the potatoes are done, use the skillet to cook whatever type of eggs you like. Add back in the meat and potatoes at the very end to warm back up.