Step 3: Bowling-out the Interior
This step is essentially bowl-turning, except you will be turning an asymmetrical piece that will remain asymmetrical. If your lathe has speed control, ease into it. I find I can safely rough-cut a piece like this at 700rpm. Your chisel will want to wander away from the center, so make your cuts carefully and perpendicular to the surface you're cutting into. Start from the perimeter and move in towards the center, resisting the outward force. If you drilled the mouth deep enough, you should break-through to it. When working with hard wood, you can leave much thinner walls than I did here. If you have the skill and a proper square chisel, make a step in the rim of the bowl to better seat the cap later on.