Preheat the oven to 180C/350F.

In a large bowl add the flours and baking powder and whisk to combine. Add the All-Bran and sugar and mix.

Melt the butter and allow it to cool slightly. Add this to the dry ingredients along with the buttermilk and vanilla. Mix well to combine.

Line a baking (or small roasting) dish on the biggest side with baking paper. A 28cm x 20cm dish or similar rectangular dish will work well here. Spread the mixture into the tin and lightly press it into all the corners.

Bake for 30 minutes until light golden brown. Cover with a  piece of tin foil from about halfway through the baking to prevent over-browning.

Remove from the oven and allow to cool on a cooling rack.

Cut the rusks into fingers of the desired thickness. Place them on a large, lined baking sheet. Space them out to allow them to dry.

Place in a low oven of around 90C-100C, preferably fan-forced, and dry for 4 - 5 hours. Turn the rusks over halfway through. Turn the oven off and let them stay inside overnight. When tested they should be dry right through before turning off the oven,