Mange Tout Soup

1 kg mange tout
1 onion
2 teaspoons salt
100 g butter
100 ml milk,
1 l stock
2 tablespoons double cream
Chop onion, fry in butter, add mange tout, add stock, simmer 30 mins, moule. Mix 1 tablespoon corn flour with milk, cook till thickens, simmer 5 mins, stir in cream.