Add the sugar to the melted butter and combine with a whisk until creamy. Break in the egg and stir it in.
Combine the flour, buttermilk powder, and baking powder, and sift. Add half of the dry ingredients to the wet ingredients and stir with a fork.
Add the rest of the dry ingredients and the water. Stir.
Optionally stir in the nuts, oats, etc.
Grease a baking pan and pour in the mixture. Bake for 50 minutes at 180℃.
Here is what it looks like when done.
Use 2 forks to divide into 16 portions. They taste better when they have a jagged cross-section.
Remove from the baking pan. (The photo shows the bottom side.)
Baking them again will evaporate the moisture. Place the cross-section sides facing up into a heat-resistant or baking tray.
Bake for 1 hour at 100℃. Flip over and bake for another hour.
They're done. Since I have a tiny oven, I stacked the pieces and baked them.
Story Behind this Recipe
I wanted to eat the same type of rusk biscuit I in South Africa. I used Tomizawa brand buttermilk powder. Instead of buttermilk powder and water, you can use 3 tablespoons of plain yogurt added to enough milk to total 100 ml.
The baking time will vary depending on your oven. If you don't have a lot of time, you can leave them sitting on top of the oven to dry naturally and then bake for 1 hour at 100℃.