Before starting the groove I used a marking gauge to traced out the edge of the channel and marked the outside corners by tracing around a coin:
I used a carving gouge to cut out most of the channel:
Carving a long groove consistently along the grain is difficult. To solve this I made a scraper and attached it to a wooden block. By running the block against the edge of the board I was able to get a smooth consistent channel:
Next I rounded off the edges of the board slightly it was done!