45-Day Dry-Aged Beef, Sweet Onions, Pickled Cherries, Feta and Colatura

• 500 g (1 lb 2 oz) 45-day dry-aged grass-fed sirloin of beef, trimmed

To make the pickled cherries, put the cherry halves in a sous-vide bag with the remaining ingredients and cook in a water bath at 64°C (147°F) for 20 minutes. Put the bag in an ice bath immediately after cooking, then set aside until ready to plate.

To make the onion purée, put the butter in a medium frying pan over low heat. When melted and lightly foaming, add the onion and thyme and