Freeze the peach slices on a shallow baking sheet lined with foil or parchment paper. Stir the 1/3 cup sugar into the buttermilk and set aside for a few minutes to dissolve the sugar. Pour the buttermilk mixture into a foil- or plastic wrap-lined loaf or other shallow pan; cover and freeze until solid.
Dump the frozen peach slices into a food processor fitted with the steel blade. Assuming the peaches are rock hard, let them sit for 15 minutes so they are slightly less than rock hard, meanwhile leaving the frozen buttermilk in the freezer. After 15 minutes, remove and cut the frozen buttermilk into chunks the size of ice cubes. Add chunks to the processor and process until the mixture is completely blended and lightened in color. You will need to stop the processor from time to time to scrape the mixture from the side of the bowl or spread and redistribute it to better engage with the processor blades; inspect for lumps of peach when you do this. When the sherbet is smooth and free of lumps, taste and pulse in preserves or additional sugar, to taste, if necessary.
Serve the sherbet immediately or scrape it into a container and store in the freezer until needed. Sherbet will retain its scoopable and spoonable texture for 2 or 3 hours before it hardens. Once it’s hard, you will need to soften it for 10 to 20 minutes in the fridge before serving, or zap it for a few seconds at a time in a microwave on defrost.
My career was sparked by a single bite of a chocolate truffle, made by my Paris landlady in 1972. I returned home to open this country’s first chocolate bakery and dessert shop, Cocolat, and I am often “blamed” for introducing chocolate truffles to America. Today I am the James Beard Foundation and IACP award-winning author of ten cookbooks, teach a chocolate dessert class on Craftsy.com, and work with some of the world’s best chocolate companies. In 2018, I won the IACP Award for Best Food-Focused Column (this one!).