Place a 12" cast iron skillet inside the oven and preheat to 450 degrees. If your skillet is too small, use a large rimmed baking sheet instead.

Place diced potatoes in a large pot covered by at least 1” of cold water and add salt. Bring to a boil over high heat then carefully add baking soda, stirring constantly to prevent boil over. Allow potatoes to boil for exactly 3 minutes then drain thoroughly.

Return potatoes to the pot and return to low heat. Allow excess water to cook off as steam for 1-2 minutes then remove from heat. Cover pot with lid and shake so the edges of the potatoes become rough and jagged.

Add melted butter, duck fat or olive oil, toss to coat and season with salt and pepper. Remove hot skillet from oven and immediately add potatoes, arranging evenly into single layer in the skillet.

Bake 35-40 minutes or until they reach desired crispiness. Stir once or twice during baking to make certain edges are browned evenly. Remove from oven and serve immediately while they’re nice and crispy.