Bring a large pot of salted water to a boil. Add potatoes and cook for about 20-25 minutes, or until almost fork tender. You want them to disintegrate when you touch them! Drain.
Heat the oil in a cast iron skillet over medium heat until hot. Add the onion and peppers. Cook for about 5 minutes, or until starting to soften. Add garlic and stir for another minute or so, until fragrant. Transfer the onion mixture to small bowl and set aside.
Add butter to the skilled with the remaining oil and heat over medium-high heat until butter foams. Add potatoes and make sure they are in an even layer on the skillet. Cook without stirring until potatoes are golden brown on bottom, about 4 to 5 minutes. Carefully turn the potatoes and repeat until browning until all sides are golden brown and crisp.
Stir in the onion-pepper mixture and carefully toss until all is combined. Season with salt and pepper to taste. Serve with some sausage and eggs for a complete breakfast!