Step 1

Place potatoes in a large saucepan of salted cold water. Bring to the boil, then reduce heat and simmer about 15 minutes or until the potatoes are just tender. Drain well, then transfer to a large bowl.

Step 2

Meanwhile, to make mayonnaise, place the egg yolk and juice in a medium bowl; whisk until pale and creamy. Slowly add the oil, whisking constantly, until mayonnaise is thick and creamy. Stir in mustard; season to taste with salt.

Step 3

Sprinkle vinegar over warm potatoes, toss gently. Season with salt and freshly ground black pepper.

Step 4

Add half the mayonnaise, half the herbs and half the onions; toss gently to combine. Drizzle remaining mayonnaise over potatoes, top with remaining herbs and onions.