Peel the potatoes and carrots. Cut them lengthwise into slices and crosswise into strips, then chop into cubes of about 1 cm (0.3 in) size. They need to correspond with the size of the peas.
Place potato and carrot cubes and peas into a saucepan, season with salt, cover with water and cook until tender (about 20 minutes). Drain and set aside to cool.
Cube pickled gherkins into the same size as the rest of the vegetables. Take your time and be precise with cutting. French salad needs to be elegant.
When the vegetables have cooled down, mix in the gherkins. Season with mayonnaise, yoghurt, mustard, lemon juice and salt. Gently stir to combine.
Leave in the fridge to set. Serve cold with roasted or grilled meat or on its own.
To make Russian salad, add cubed and cooked gammon too.