Remove any stalks or leaves from the kohlrabi bulb. Trim off the ends with a chef's knife. If you have a very large kohlrabi, slice it in half.
Use a paring knife to remove the tough outer skin from each half.
Slice the kohlrabi into 1-inch rounds. If you want smaller pieces, dice those rounds into cubes. For raw preparations, thinly slice the kohlrabi with a mandoline or grate it.
To make basic roasted kohlrabi, toss kohlrabi cubes in some olive oil, salt, and pepper. Spread out on a lined baking sheet, and roast for 30 to 35 minutes at 450°F, flipping halfway through.
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Notes
Kohlrabi skin is tough and sometimes rubbery, but it is edible. If you want to keep the skin on, you can.
Store kohlrabi bulbs wrapped in a damp paper towel in a loose-fitting plastic bag in the fridge for up to a week.