Usually boiled, these baby beetroots are here roasted with chunks of red onion and tossed in a garlic mayonnaise. Raw onions and a garlic sauce? The combination sounds strident, but these are sweet mild onions and the garlic is cooked before being puréed and incorporated into the mayonnaise. The result is a successful balance of firm chunks of beet and crunchy onion, the aioli giving a moist rich gloss to the dish. This is a salad to serve when the new-season’s garlic is available.