I grew up on a farm that had an old growth walnut tree. Dad had it cut down when he sold the farm as I was finishing college. He had it cut into boards of different sizes and I still have a few 12+ inch wide ones, including a few with grain figure like yours. I made several laptop computer "lap" holders back in the 90's. Very meticulously I cut 1 inch thick boards in half (thickness wise) on a TS. 3 3/4" deep on the top and bottom and slowly cut the middle with a Japanese pull saw. Sanded and looked great like yours. My friends loved them. I still have mine somewhere.
You brought back old memories!