1. Oven at 180°C.
2. In a large mixing bowl or Kenwood mixer, beat the buttermilk, oil, melted butter and vanilla essence together.
3. Mix in the Large Tiger Flakes and allow to soak together for 5 minutes.
4. Mix the flour and the baking powder together in a separate bowl.
5. Add the sugar to all the wet ingredients and blend in well.
6. Lastly add the blended flour and baking powder in two batches. Mixing in well in between.
7. Mix well for a minute or two until the ingredients are all well blended.
8. Grease a large baking tray.
9. Pour the rusk mixture onto the baking tray and spread it out evenly.
10. Slice lines through to the base of the rusk mixture to the size you wish your rusks to be.
11. Bake in the oven for 30 minutes.
12. Allow the rusks to cool for about 15 minutes.
13. Slice the rusks.
14. Divide the rusks onto two large baking trays by placing the rusks on their sides to dry out.  See further to dry out.
15. Place the two trays in the oven to dry out for about 3½ to 4 hours in a pre-heated oven at 75°C thermo fan or at 100°C without the thermo fan.  (You can also alternate the position of the two trays half way during the drying time.)  
16. After 3½ hrs, test a rusk first to see whether they are crispy throughout. (Careful it is hot!)  Bake/dry out a little longer if not crispy right through.

A great tip for a tart crust:  Reserve all the crumbs that may collect on the baking tray or in the baking tin whilst storing.  These crumbs can be stored in an air tight jar or container and used for later to make a healthy mixed cookie/butter base.  If you need more crumbs, simply place a few more oat rusks into a food processor and blend into crumbs.  These oat rusk crumbs make the most delicious, tasty crust base for lemon meringues, fridge cheese tarts, etc.,  (180 to 200g oat rusk crumbs blended with 90 to 100g melted butter).