Place the cold milk, corn flour and bay leaf into a poaching pan.
Heat the milk gently and stir until the liquid thickens slightly to a white sauce consistency, about 5 minutes and then season to taste.
Place the fish fillets into the poaching pan and cover with a lid. Allow the fish to poach gently, about 5 minutes, checking for when the fish has nearly firmed up fully.
Remove the bay leaf, add the drained butter beans and heat them through whilst the fish fully firms up, about a further 3 to 4 minutes.
Remove the fish fillets and butter beans to serving plates and garnish with the chopped fresh parsley.
Notes
Suggested serving with new baby boiled potatoes and / or a salad.