Roasted vegetables are fashionable and this is not undeserved , they are delicious. The oven time to roast a whole celeriac in the oven is approximately 3h, so economically not so great. My easy solution? Wash the celeriac thoroughly and remove the roots. Halve in two equal parts. Spread some olive oil on top, some rough salt and dried thyme. Put the halves on baking paper and roast in the oven at 180° for approx 1 1/2h. If they risk to burn ( only skin is not a real problem) cover them with baking paper towards the end. They really have to become well-cooked (check with a knife). Serve as a side dish, as an appetizer or as full meal. Experiment with other herbs, awesome!! The taste is a bit nutty and sweet. A must-try!