Steam the vegetables separately until soft.
Toss the cooked potatoes, turnips, carrots, string beans and peas together in a bowl and season with salt.
Fold in the mayonnaise (see recipe below) and turn out to a romaine leaf-lined platter.
Garnish with the cubed, cooked beets.
Mayonnaise: Combine the yolk.
mustard and salt in a mixing bowl and whisk to mix well.
Drop by drop, add the oil until the mayonnaise starts to emulsify.
Whisk in the remaining oil in a thin stream.
Add your lemon juice, check for salt and pepper.