This recipe is adapted from Delia's Complete How To Cook
Basic mayonnaise mixture (see related recipe below)
75g fresh spinach leaves
40g watercress leaves
40g flat leaf parsley leaves
2 tablespoons fresh tarragon, chopped
1 tablespoon snipped fresh chives
1 tablespoon lemon juice (or more to taste)
Salt and freshly milled black pepper
Rinse the spinach, watercress and parsley under cold water and put these into a medium saucepan.
With the heat turned to medium, stir the leaves around until everything has just wilted, then tip them into a colander and rinse under cold water to keep the colour.
Now squeeze out the excess moisture very carefully, thoroughly pressing and squeezing with a wooden spoon. Then transfer the cooked leaves to the mayonnaise in the blender with the chopped tarragon and chives and whiz until smooth and green.
There will be some fine specks but that's okay.
Now do a bit of tasting and season with lemon juice, salt and pepper.