850g/1lb 14oz floury potatoes, such as Maris Piper or King Edward, peeled and cut into quarters
2 garlic cloves, crushed
3 onions, halved and sliced
2 tbsp chopped fresh parsley leaves
100g/3陆oz baby spinach leaves
125g/4oz plain flour, plus extra for rolling
flaked sea salt and freshly ground black pepper
pinch freshly grated nutmeg
1 tbsp sunflower oil
125g/4oz wholemeal flour
150g/5oz butter
25g/1oz butter
175g/6oz mature cheddar, coarsely grated
250ml/9fl oz double cream
1 free-range egg, beaten