Decided to do the groove in the bread boards on the router table with a slot cutter bit
And then to do the tounge on the end grain of the top with a rabbet bit. I often find the parallel set up bars used with the machinist vice on my bench top mill come in handy for set ups. They are 1/8” thick, so in this case two of them inserted in the groove with a feeler guage leaf was snug as a bug in a rug. This allowed me to match the rabbet bit height to groove bottom.
the result was a nice snug fit…. which, do to the slight warp of the panel, needed a little love tap from my assistant.
and here’s the completed top, ready for a final sanding.
-- Pine is fine, but Oak's no joke!