Peel the kohlrabi bulb until you reach the inner, semi-translucent heart. This is the tenderest part of the plant, and will soften when cooked.
Peel and cube kohlrabi and sweet potatoes. Toss with olive oil, herbs, and spices.
Bake at 400 degrees F for about 45 minutes, until kohlrabi and potato are fork-tender. Turn occasionally to keep moist while baking.