Melt the sugar and butter in the microwave. Add the dry ingredients. Mix the buttermilk vinegar and eggs together. Add to the mixture.
In a rusk pan or large oven pan, place the mixture in the pan. Level the mixture evenly. Bake at 160 degrees Celsius for 1 hour. Cut when cooled and dry overnight in oven on a very low heat with the door slightly ajar. You can use a wooden spoon to keep the door open.