Wash the parsnips (and possibly the carrots) thoroughly with a brush and peel them if necessary. Then cut into thin, elongated pieces.
Peel the onion, cut into small cubes and fry in the butter until translucent. Then add the parsnips and season with thyme, parsley, sugar and salt to taste.
Cook the whole thing gently for about 10-15 minutes. Add some water or wine. Season to taste with a little sugar and stir well before serving.
For this you can e.g., Serve wiener sausages or mince cakes with potatoes