For the sauce: heat the oil in a large pan and fry the onion and garlic until soft. Add the tomato paste and cook for 5 minutes. Add the soy sauce and Madeira bring to the boil, and then add the stock and barley. Simmer for 25 minutes until the barley is soft.
For the vegetables: heat the stock in a pan and bring to the boil. Add the parsnips, carrots and celery to the pan and cook until tender, then remove from the pan. Cook the potato slices until tender and remove from the pan.
Preheat the broiler.
Assemble the hot pots by layering the parsnips, carrots and celery in individual pie dishes. Spoon over the sauce then add the thyme. Toss the potatoes in the olive oil, season well with salt and pepper then layer on top of the vegetables.
Put under the hot broiler until the top is browned.