Gently soften the leeks in butter and oil
in your largest pan for 15-20 mins until
almost meltingly soft. You can soften the
leeks up to a day ahead, then just reheat
in the pan before continuing the recipe.
Stir in the stock, bring to a simmer and
cook, stirring occasionally, for 5 mins. Stir
in the peas and spring onions for 3-5 mins
more until the peas are defrosted and
cooked through, then season and serve.