Cos Salad with Peas and Parmesan

• 2 heads of Cos (Romaine) lettuce
• 1 teaspoon Dijon mustard
• 1

Trim the green tops of the lettuce and remove any blemished outside leaves before cutting into 1cm (½in) wide ribbons down to the stalk. Soak briefly in a bowl of cold water, then spin-dry and place in a salad bowl.

Make the dressing by whisking the mustard, yoghurt, lemon juice and seasoning together in a bowl before adding the two oils.

Pod the peas and scatter them over the s