First, glue two pieces of ¾-inch hardwood plywood to each other. Next, cover the front edge with a ¾-inch-thick by 1½-inch-wide strip of solid wood. Attach the strip with glue and finishing nails, making sure to stagger the nails above and below the glue line. After the glue dries, sand the strip flush with the plywood, and round over its edges. The longest shelf I've made this way is 56 inches, but another 3 inches shouldn't be a problem.