100g/4oz chestnut mushrooms, brushed to remove any grit, sliced
400g/14oz leeks, trimmed and thinly sliced (225g/8oz trimmed weight)
lightly dressed fresh green salad, to serve (optional)
1 tbsp wholegrain or Dijon mustard
1 tsp English mustard powder
pinch crushed dried chillies (optional)
100g/4oz leftover mashed potato
100g/4oz plain flour, plus extra for dusting
salt and freshly ground black pepper
2 tbsp olive oil
75g/3oz chilled unsalted butter, diced
50g/2oz Cornish blue, Stilton or Gorgonzola (or a similar vegetarian blue cheese), diced
75g/3oz mascarpone