°peanut oil  
°2 tablespoons sweet unsalted butter
°1 pound Idaho Russet or red potatoes 
°salt water
°sweet onion 
°Salt & pepper to taste

Place a heavy 9-inch cast iron skillet over medium heat (just a little more than medium on the stovetop).
Pour the oil into the pan and add the butter as well. Let it heat until the oil is glistening on the surface - not smoking - if it starts to smoke, remove from heat and let cool until shiny again.
Cut the potatoes into pieces of the same size - chips or cubes - of your choice.
While chopping, place in 4 cups of water containing 2 tablespoons salt mixed in.
Cut the onions into larger pieces than the potatoes.
After 5 minutes, drain the potatoes well and dry them with paper towels
When the oil is ready (shiny) put the potatoes and onions in the oil. Don't crowd the potatoes. If there isn't enough room for them to put side by side, let some of them cook, remove to drain on a paper towel and then cook the rest.
Cooking for 4 min on 1 side then flip and cooking for other 2-4 minutes on other side.
Draining on a paper towel. Salt and pepper once removed from the oil
Decorate and serve hot.

Enjoy !