Preheat the oven to 425° and position a rack in the lower third of the oven. In a large shallow bowl, whisk the flour, baking powder, baking soda, sugar and fine salt. Add the chilled butter and use a pastry blender or 2 knives to cut the butter into the flour until it is the size of peas. Add the grated zest and the poppy seeds. Stir in the buttermilk just until the dough is moistened. Lightly dust a work surface with flour. Turn the dough out onto the surface and knead 2 or 3 times, just until it comes together. Pat the dough into a 1/2-inch-thick disk.