It's not hard to do, Rick. Find the center of the bowl and drill a hole for a screw center. Turn a recess that you can expand your chuck jaws into. Using a recess here over using a tenon saves some wood. Remove just enough wood for the jaws, that way you still have the center mark for when you finish the bottom. Turn the bottom close to the final shape. Your going to remount it later to turn away the recess. Take the piece off the screw center and remount using the recess. Turn the the rim and the inside of the bowl to a finish and sand. Again, it helps to use the tailstock as much as possible while turning. Take the piece off the chuck. Reverse mount the piece between centers. You can put a stub in the chuck with something soft between the stub and the inside of the bowl or if you have a faceplate that will fit inside you can pad it to protect the bowls interior. Now bring up the tailstock to hold everything in place. Finish turn the bottom removing the recess and leaving a small stub at center to be carved away and hand sanded. By the way I use a tailcenter without a point, again so I don't have to loss wood. It's hard to see in the picture, but there is a small concave area on the bottom so it will sit flat.