Brussels sprouts with chestnut and sage butter

Put the butter, chestnuts and sage in a bowl and mix well. Scrape the mixture onto a large piece of greaseproof paper and shape into a log. Wrap in the paper and refrigerate until firm. Cook the sprouts in salted boiling water for 10-12 minutes until tender. Drain. Cut the chilled butter into slices. Toss 4 of the slices with the sprouts until they are well coated in butter, and season well. Arrange the remaining slices on top and serve at once.