Cubing potatoes is a great way to ensure that they are seasoned as much as possible. This is particularly important if you are intending to sauté the potatoes in a frying pan. While it is possible to cube potatoes with a knife, to get uniform, restaurant-quality potato cubes, you should use a mandoline slicer. Mandoline slicers have incrementally adjustable blades, meaning you can get almost any size potato cube you want.
Adjust the cutting blade depending on what size potato cube you want. Aim to make the cubes at least 1/8-inch thick; otherwise the potatoes may disintegrate during cooking.
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Using the hand guard, push the potato lengthwise over the mandoline's blade. The slices of potato will be caught in the holder beneath the blade.
Take out the slices and re-form them into the original shape of the potato. Run the potato through the slicer again, this time on its side at a 90-degree angle to the first time. Your potato should now be cut into even strips.
Reform the potato once again and run it through the slicer a final time, pushing the strips of potato vertically through the blade. Uniform potato cubes will be collected in the mandoline's holder.
Use care to avoid cutting yourself on the mandoline's sharp blades.