Feel free to substitute blackberries, olalliberries, raspberries, or roughly chopped fresh cranberries for blueberries if you like. If fresh berries aren't available, feel free to use frozen ones, adding them to the batter straight from the freezer (no need to defrost).
In a large bowl, use electric beaters or a whisk to cream the butter and sugar until smooth. Add the lemon zest and the eggs and whisk until incorporated. Add the buttermilk and mix again until incorporated.