Melt the butter in a small saucepan and stir in the garlic, thyme and plenty of nutmeg. Season with salt and pepper.
Slice the potatoes, carrots, celeriac and swede as thinly as possible. (A food processor with a slicer attachment or a mandoline is ideal). Layer all the vegetables in an ovenproof dish, drizzling over a little of the flavoured butter as you assemble the dish.
Pour over the hot stock and cover the dish with foil. Place on the lower rack of the halogen oven.
Set the temperature to 250°C (482°F) and cook for 1–1¼ hours until the vegetables feel tender when pierced with a knife. Remove the foil and bake for a further 15 minutes or until the surface is golden. Serve with roast meats or poultry.