For doing just the top piece, I see a raised panel bit followed by a cove bit of just the right size. Careful setting up of the router table with each bit and a fixture to hold the piece perfectly square to the fence as you pass it through. It's going to take a few pieces of dimensioned scrap to get the settings right. Of course, a shaper could do it too, but with similar set up difficulties.
Cutting the stock the correct width and making two passes, then cutting into squares and making the other two passes would at least make part of the job a little safer. Several feather boards needed for this.
Central North Carolina