The slimmer the spring onion, the milder the flavour. For the best crunch and maximum taste choose big bulbs. If they're slimy, they're past their best. Spring onions are essential in potato salad, and this recipe makes enough for six people. Cook 450g (1lb) new potatoes in boiling salted water until tender. Drain well then tip into a bowl. Add 2 finely sliced spring onions, 2tbsp each Greek yogurt, mayonnaise and wholegrain mustard and a squeeze of lemon juice. Season well and toss together.