A prune-based marinade helped us transform an economical eye round into a tender and juicy roast. The sugars in the prunes and ketchup create a nicely caramelized crust, while the salt and soy sauce provide seasoning that flavors the meat throughout. The anchovies may be an unexpected ingredient here, but they add rich umami notes without any trace of fishiness. To boost the marinade’s effect, we trim the silver skin and also poked the meat repeatedly with a fork. The roast beef tasted best after marinating for 48 hours, but 24 will work, too. Serve thinly sliced with fresh horseradish sauce for a clean, contrasting bite.