Place oil in a large, deep, pan, Dutch oven or deep-fryer. Attach a deep-fry thermometer to monitor the temperature and heat oil to 350F.
While oil is heating, wash and peel potatoes and remove any dark spots.
Using a mandoline slicer fitted with the julienne blade and slice potatoes into matchsticks.
Place sliced potatoes in a large bowl of ice water for 10 minutes.
Remove potatoes from water bath and place on paper towels or clean dish cloths to dry completely. Pat the potatoes dry or use a salad spinner, if available. The dryer the potatoes, the less excess splattering there will be.
The next step is crucial to not having a disaster (or fire) in your kitchen. Do NOT add too many potatoes at one time.
Once oil is 350F, place dried potatoes (1-cup at a time) in the oil and stir to separate them. Adjust temperature to keep it as close to 350F as possible.
Fry 2½ - 3½ minutes or until dark golden brown – watch closely and stir often..
Transfer cooked potatoes with a slotted spoon to a paper-towel covered surface and season with salt and black pepper. If desired, add other spices or seasonings at this time.
Repeat process until all potatoes are fried.
Allow potatoes to cool completely, then store in an airtight container. The potatoes will stay crispy and crunchy at least 3 days and probably more.
Serve as is or with a side of sweet, hot mustard, bbq sauce or dip of your choice.