Place the walnuts in a medium bowl; drizzle with butter. Toss to coat. Add the rosemary, salt, and pepper; toss to mix. Spread the nuts out in a 15x10x1-inch baking pan. Bake until the nuts smell toasty and are just lightly browned, 12 to 14 minutes, stirring halfway through.
Transfer the nuts to a bowl (it can be the same one they were first mixed in), add the dried cherries, and toss to mix. Serve warm, or let cool, then transfer to a serving bowl or store in an airtight container for up to 5 days.