Preheat oven to 350 degrees F. Grease and flour a 9x5x3-inch loaf pan; set aside.
Trim the ends off the zucchini and thinly slice 3 to 5 rounds from one end of the zucchini and reserve for garnish. Shred the remaining zucchini, toss with 1 tablespoon of granulated sugar and place in a colander. Allow to drain for 30 minutes, then gather it in a clean kitchen towel and squeeze out any excess water.
In a large bowl, whisk together the flour, sugar, cornmeal, baking powder, baking soda and salt. In a medium bowl, whisk together the butter, eggs and buttermilk. Gently stir the zucchini into the butter mixture. Pour the wet ingredients into the flour mixture and use a rubber spatula to gently fold together until no traces of flour remain. Pour the batter into the prepared loaf pan and top with the reserved zucchini slices.
Bake until the bread is golden brown and a tester inserted in the center comes out clean, about 55 to 65 minutes. Let cool in the pan for 10 minutes, then turn the loaf out onto a wire rack to cool completely. The bread can be stored at room temperature, wrapped in plastic wrap, for up to 3 days.