4 large ripe tomatoes, peeled and chopped (or 1 x 400g tin chopped plum tomatoes)
350ml/12fl oz chicken stock
600g/1lb 5oz leftover roast chicken, shredded
16 black olives, stones removed, halved
2 tbsp chopped fresh parsley
50g/1¾oz Gruyère cheese
For the potato topping
1.5kg/3lb 5oz floury potatoes, such as King Edwards, peeled
5 tbsp double cream
2 free-range egg yolks
salt and black pepper
For the topping, boil the potatoes in salted water until tender. Drain and push through a potato ricer, or mash thoroughly. Stir in the butter, cream and egg yolks. Season and set aside.
For the filling, melt the butter in a large pan. Add the shallots, carrots and celery and gently fry until soft, then add the garlic. Pour in the wine and cook for 1 minute. Stir in the tomato purée, chopped tomatoes and stock and cook for 10–15 minutes, until thickened. Add the shredded chicken, olives and parsley. Season to taste with salt and pepper.
Preheat the oven to 180C/160C Fan/Gas 4.
Put the filling in a 20x30cm/8x12in ovenproof dish and top with the mashed potato. Grate over the Gruyère. Bake for 30–35 minutes, until piping hot and the potato is golden-brown.