Rip three boards to the desired width.
Set the two legs on edge on a flat surface and set the face board on the legs. Check for a good fit. If the boards fit well, apply glue to the edge.
Nail the face board to the leg every 8 to 10 inches with 2-inch,18 gauge nails. If you are nailing by hand, drill pilot holes and use 6d finish nails.
Apply glue to the edge of the other leg and nail the face to the leg.
Clamp the face to each leg with wood clamps. Place the clamps 12 to 16 inches apart. Keep the clamps on for at least a 1/2 hour before removing them.
Scrape off the excess glue with a chisel and sand the joint smooth with a palm sander.