2 tbsp chopped chives
1 onion, finely diced
1kg/2lb 4oz Desiree potatoes, peeled and cut into large chunks
200g/7oz plain flour
salt and white pepper
75g/2陆oz cold unsalted butter, cut into roughly 1cm/陆in dice
25g/1oz mature cheddar, finely grated
375g/13oz mature cheddar, grated
1 free-range egg, beaten, to finish
50ml/2fl oz milk
25g/1oz parmesan (or vegetarian alternative), finely grated
75g/2陆oz white vegetable fat, cut into small pieces