for carving things like spoons or bowls out of wood it's usually suggested that you use something called a "hook knife" to get the round sort of hollow shape
they cost about 20 quid
I didn't want to spend 20 quid, so I got a set of 3 ring spanners from poundland and spent some time with a dremel (other rotary tools are available) and made this ring knife type thingy that does the job fine