- Preheat the oven to Gas mark 7, 220°C/425°F.
- Heat a large, shallow, non-stick frying pan and dry fry the mince until brown. Add the onion and cook for a further 2-3 minutes.
- Add the mustard, stock, herbs and seasoning. Bring to the boil, reduce the heat, cover and simmer for 15-20 minutes, stirring occasionally. Add the sweetcorn and stout or ale and cook uncovered for a further 5 minutes. At this stage stir in the instant thickening granules, if required.
- Meanwhile, heat the butter and oil in a large, shallow frying pan and fry the sweet potato and turnip slices in batches for 3-4 minutes on each side, then drain on absorbent kitchen paper.
- Place 4x10cm/4inch metal cook’s rings on a foil-covered baking sheet. Line the base of each ring with a combination of sweet potato and turnip slices. Spoon over a quarter of the mince mixture equally.
- Repeat the process twice, finishing each ring with a layer of sweet potato and turnip slices.
- Bake in the oven for 10-12 minutes. Remove from the oven and using a fish slice transfer to a serving plate. Leave to rest for 2-3 minutes before removing the ring.