Mix wheat flour, plain flour, muesli, baking powder and salt in a bowl.
In a big bowl, whisk together oil, brown sugar and thick buttermilk.
Now add all the dry ingredients to the wet ingredients and make a dough.
Grease a 9 * 9 inch baking tin and add the dough to it. Spread the dough evenly in the baking tin with the help of hands. A slightly bigger or smaller baking tin can also work. Now bake this in a preheated oven at 170 degree for 30 minutes.
After 30 minutes switch off the oven and take out the baking tin and let it cool for 10 minutes. Now turn it over to a wire rack and let it cool for 30 minutes.
Now take this rusk base on a chopping board and cut into pieces. Arrange the pieces on a baking tray and bake it in a preheated oven at 140 degree for 20 minutes.
Now turn over the pieces and again bake it at 140 degree for 20 minutes. Repeat the process until they are baked properly and completely dry.
Now let the rusk cool down completely and store it in an airtight container.
