750g/1lb 10oz floury potatoes (Maris Piper or King Edward), peeled and cut into 2cm/戮in cubes
1 onion, finely chopped
2 tbsp chopped parsley
salt and freshly ground pepper
250g/9oz plain white flour
1 tsp bicarbonate of soda
1陆 tsp table salt
250g/9oz wholemeal flour
50驳/1戮辞锄 butter, plus extra to serve
425ml/戮 pint buttermilk
1.2 litres/2 pints full-fat milk
450g/1lb undyed smoked haddock loin, skin and any bones removed