I don't know where rusks originally came from - I think the Dutch brought them - or something similar - to South Africa years ago. My memories of eating rusks involve crunching them on holiday in South Africa, eating them early in the morning in Nyanga, even trying Aunty Heather's rusks in Bindura when I was a kid.
Here is my mom's recipe (with a few healthier substitutions) - the ones that taste like home, and it uses our homemade muesli recipe. . But you can use anything - oats, seeds, coconut, nuts, bran....be creative :)
1C melted marg/butter
In a separate bowl mix:
3 & 3/4C self-raising flour
1 tsp salt
2 1/2tsp baking powder
2 1/2 C muesli
Add the wet and dry mixture together - mixture will be sloppy.
Grease a 13x9" pan and plop the mixture into large balls in the pan (fit's about 12 balls).
Bake on 350 degrees for 45-60 minutes, until golden and a knife comes out clean.