Preheat oven to 160ºC and grease a 28cm x 38cm cake tin or casserole dish.
Warm the milk in the microwave only enough to take off the chill. Add the lemon juice or vinegar and allow to stand while you continue.
Combine all dry ingredients in a large mixing bowl. Add the butter and rub into the dry ingredients until the mixture is like breadcrumbs.
Stir the milk mixture and whisk in the egg, add to the flour and combine well.
The mixture will be very loose, it shouldn’t be too sticky. If it is too sticky, just add a tablespoon of flour at a time until it is less sticky. You don’t want a dry dough.
Roll the dough into balls, about the size of a naartjie or for those of you who are not South African, a clementine. Flour your hands before rolling.
Bake for 20 minutes. Start 20min timer Turn the oven down to 150ºC and bake for a further 30 to 35 minutes. Start 30min timer The rusks should not be golden, but rather blonde on top.
Remove the rusks from the tin immediately and turn onto a wire rack. Pull them apart while they are warm and leave to cool completely.
Once cool, place rusks, still on the wire rack into an oven set at 50ºC for about 6 to 8 hours.
Store in an airtight container.