I used to use a mandoline to make beet chips, slicing them into paper thin circles then baking them until crunchy like potato chips. Now I take a cue from my mom's far less fussy technique, where she just cuts the beets with a knife as thinly as possible--not only is this more practical than busting out a mandoline, it actually yields a more delicious result. The beets are crisp on the edges and slightly chewy in the center. So good! —Posie (Harwood) Brien
Preheat the oven to 400 degrees F. Drizzle half of the olive oil over two baking sheets and rub it around the oil the sheets (depending on the size of your beets, you'll need to use more than two baking sheets).
Using a very sharp knife, slice the beets into thin slices. Don't stress about making them perfect! Just cut them as thin as you can without going nuts. Keeping them uniform is ideal because they'll cook evenly, but it's actually delicious when some are thicker (and chewier) and some are thinner (and crispier).
Arrange the slices in one layer on the baking sheets. You don't want the beets to overlap, so use as many baking sheets as you need to avoid overlapping. Drizzle the remaining olive oil over the beets and rub lightly with your hands to spread the oil. Sprinkle salt and pepper over the top of the beets.
Bake for 10-15 minutes. The longer you bake, the crispier the beets will be, and I like keeping them a bit chewy. Remove from the oven, let cool slightly, and eat! They're great on their own and delicious with a dip like tzatziki.