I have done a quick WIP on it as below.
I started with a nice Oak board 36" x 7 1/2" that I had lying about for some time.
It is sanded all sides because the back will be left as plain wood.
The lines in this piece are all done with a freehand Router fitted with a Dovetail cutter .They are done with a Dovetail cutter because that gives it an undercut that looks good
First the vertical grooves are cut and making sure I did not lift the Router out before the completion of the cut to avoid break out.
Then the horizontal lines ar cut again making sure I don't lift the Router early