Cook the carrots and potatoes in a pan of boiling salted water for 4 mins, then throw in the peas and cook for 4 mins more until all the vegetables are tender. Drain, cool for a few mins, then tip into a bowl with the cornichons, mayonnaise and parsley, if using. Mix well and season to taste. Delicious with leftover roast beef or lamb, wedges of pork pie or cold sliced ham or chicken