1 small onion, thickly sliced
800g/1lb 12oz medium potatoes, peeled and cut into quarters
40驳/1陆辞锄 plain flour
40驳/1陆辞锄 butter
40驳/1陆辞锄 butter, cubed
100g/3陆oz mature Cheddar cheese, grated
400ml/14fl oz whole milk
3 tbsp milk
200g/7oz large raw prawns, peeled
500g/1lb 2oz thick white fish fillets, preferably cod, haddock or pollock, skinned
150g/5陆oz frozen peas