1. Boil potatoes in a large saucepan until tender, then drain and leave to cool.
2. To make the dressing, put the avocado, sour cream (or yoghurt), lemon juice and garlic in a bowl and mash together with a fork until smooth and well mixed.
3. In a large serving bowl, add the potatoes, onions, avocado dressing and any of your other salad ingredients (eg, peas, chopped boiled eggs or gherkins) and gently mix together.
Notes
If the avocado dressing is too thick, stir in 2 teaspoons of milk.
This salad can be eaten warm. To do this, add the dressing while the potatoes are still hot and serve immediately.