Preheat oven to 150ºC/300ºF/gas mark 2.
In a large bowl, add the first four cut vegetables, and carefully toss with couple tablespoons of oil and pinch of salt and pepper to coat. Transfer the contents into the bottom of a Dutch oven.
In the same bowl, coat the exterior of the celeriac with oil, more salt and pepper and place on top of the vegetables in the Dutch oven.
Add liquid and bay leaf, then cover and roast low and slow for 3 1/2 to 4 hours until done. You can tell when it’s finished when you can pierce through the celery root with a long skewer easily.
Remove from the oven, carve slices of celeriac monster and serve with the vegetables. Garnish with the fresh herbs and parsley, and serve with horseradish, if desired.