These chips may take less time (or longer) depending on how accurate your oven temperature is. Mine is extremely inaccurate and cooks very unevenly, so it’s always a gamble when they’ll be ready. I keep an eye on them so they don’t get too burned!
Preheat oven to 400 degrees F.
Place parchment paper over two cookie sheets or baking pans.
Wash and scrub your sweet potatoes. Using a mandoline, a food processor, or your own hand and a very sharp knife, cut round chips as carefully and thinly as you can. I recommend wearing a cut-proof knife glove if you have one.
Optional: soak the cut chips in a bowl of ice water for 20 minutes. This apparently helps them crisp up, but if you don't have time, it's not absolutely necessary.
Put the chips in a bowl and toss with the melted oil and your choice of seasonings. Adjust seasonings if it looks like they aren't fully coating the chips.
Place the chips on the parchment-covered cookie sheets, and make sure they do not overlap! This prevents them from becoming crispy. After the sheets are filled (this may take more than one batch), put them in the oven and set a timer for 20 minutes.
Watch the chips to make sure they aren't cooking too quickly or unevenly. After 20 minutes, take them out and flip them carefully, then put them back in the oven again for 20-25 minutes. Watch them again to make sure they aren't browning too quickly, usually the ones on the outside of the pan cook much quicker.
They're ready when they nice, browned and crispy!