When I turn a bowl on my lathe, I use dead or downed trees: green wood turns better, I like the subtle warps that come with aging, it's environmentally sustainable, and it's almost always free. In milling a log into rough bowl shapes, though, it's generally advised to cut around the pith, which warps, checks, and cracks faster and bigger than any other part of the log.
Instead of chucking this middle section, I started making these kitchen blocks. Too pretty to be just cutting boards, but too versatile and durable to simply be serving pieces. Stock rotates as I mill new logs- currently spalted maple, birch, black locust, and white oak.
Almost never square (I try to maximize the thickness area) but as flat and smooth as can be, these are finished with food-safe 100% pure tung oil and ready for your kitchen!