Measure all ingredients and keep them ready.
Line an 8 inch square baking tray with parchment paper.
Preheat oven to 180 degrees Celsius.
In a mixing bowl, add the all purpose flour, baking powder and salt to make self raising flour.
Take milk in another small bowl, add vinegar/ lemon juice and set it aside for 5-10 minutes. This will turn into buttermilk.
Add baking powder and salt to the self raising flour. Thereafter, add the butter and rub in to get a crumb like texture.
Add all the other dry ingredients and mix well.
Lastly, add the buttermilk and get the ingredients together to form a lumpy dough.
Spoon this mixture into the lined tray and level gently with a spatula.
Bake for 45-50 minutes till toothpick inserted in the centre comes out clean.
Take out from oven and let the whole bar cool on a wire rack.
Thereafter, slice into 15 pieces (or as desired). Use a sharp knife.
Place these pieces on a oven wire rack and dry @90-100 degrees for 2.5 - 3 hours. ( Leave the oven door slightly ajar.) Rusks are done when they are crisp and not spongy.
Dunk your rusk in hot cup of tea!