Use the Easel project at the link below to cut for identical sides from 3/4" lumber. The project is set up to to cut two at a time, but you could cut all four at once if your lumber is wide enough. Sand!
Note: I recommend you confirm the thickness of your lumber and make adjustments to the length of the finger joints as necessary. Also measure the thickness of the plywood that will be used for the bottom and adjust the width of the groove if necessary.
Finish sand the serving tray to soften any sharp edges and remove any tool marks. Apply your choice of finish. I recommend 4-5 coats of Deft Clear Wood Finish Satin Spray Lacquer.