1. Preheat the oven to 215ºF (100ºC.) Lightly grease a 9-inch (23 cm) square cake pan.
2. In a large bowl, whisk together the all-purpose and rye flours, the baking powder, baking soda, and caraway seeds.
3. In a spice grinder, or mortar-and-pestle, grind the fennel and anise seeds into they are close to finely ground, but they can still have a bit of texture to them. Whisk them into the four mixture until they are evenly dispersed.
4. Make a well in the center of the dry ingredients and pour in the buttermilk and dark syrup. Stir the mixture just until the dry ingredients are completely moistened, but don’t overmix.
5. Scrape the batter into the prepared pan and bake for 30 minutes.
6. After 30 minutes, increase the heat of the oven to 325ºF (160ºC) and bake for another 30 minutes, or until the bread feels just-cooked in the center when you press it. (If using an instant-read thermometer, it should read 190ºF, 88ºC.)
7. Remove the bread from the oven and as soon as it’s cool enough to handle, remove the bread from the pan and let it cool on a wire rack.