I made em by starting with square stock and pre-drilling. A Forstner bit would be good. You can use a spade but then you will weaken the bottom or just go through.
Brings me back to 6th grade shop class, Mr Green says" Now Treemandan, we don't make those here." I also won a prize for spinning and wiring a lamp. The thing was like a first place trophy itself it was so huge.
They wanted to keep it for the main office and I said " You would think I would let you considering the ammount of time I spent in here on dentention but NO!"