Melt sugar and butter together in a small bowl.
Mix dry ingredients in an extra large bowl, add melted butter, buttermilk, and eggs and mix well until mostly combined.
Tip onto a clean working surface and knead until the batter is well combined.
Split the dough between two steel ovenproof pans. Note: there's no need to line the tray with butter or cooking spray. Cut/section the dough with a knife before you bake them for 40-45min at 180℃ / 356℉. Note: you can cut them as small or as big as you prefer them. You can bake in batches or simultaneously, depending on your oven rack setup.
Cut/section the baked rusks again, loosening them and carefully break the pieces apart. Spread evenly on a tray and bake at 90℃ / 194℉ for 2-4hrs or until they’re fully dry. Note: don’t fully close the door of the oven, just place a dry cloth in between the oven door and the oven to allow additional moisture to escape.
Place the dried rusks in an airtight container. If might start softening over time, if so, just pop them back in the oven to dry out for an hour or so and you're good to go!