Peel the sweet potato, cut it into large chunks and boil it in a saucepan of salted water for 20 minutes, or until the sweet potato is soft. Strain, and mash. Chop the garlic, celery, onion and carrot, and sauté in a pan using a little olive oil over a medium heat with a pinch of salt and cumin.

Peel the sweet potato, cut it into large chunks and boil it in a saucepan of salted water for 20 minutes, or until the sweet potato is soft. Strain, and mash. Chop the garlic, celery, onion and carrot, and sauté in a pan using a little olive oil over a medium heat with a pinch of salt and cumin. Meanwhile, chop the seitan using a food processor or a knife. When the vegetables are soft, add the seitan and the bay, and stir continuously so that it doesn’t stick. Cook for 5 minutes. Add the wine and cook so that the alcohol evaporates, still stirring. After two minutes, add the soy sauce and the apple concentrate. Cook for 2 further minutes and remove from the heat.

To make the pie, cover the base of a roasting tin evenly with the seitan mixture, and spread the purée on top. Cook in the oven at 180ş for 30 minutes.