Photo credit: G. Drakopoulos - Food Styling: T. Webb
- Preheat oven to 160* C (320* F) Fan.
- Brush a 22 cm round cake pan, lightly, with some oil.
For the toasted walnuts
- Preheat oven to 160* C (320* F) Fan. Line a baking sheet with some parchment paper. Place the walnuts on the baking sheet. Bake for 10-13 minutes, until they turn golden and crunchy. Remove quickly from the oven and set aside to cool.
For the caramel
- Add the brown sugar, heavy cream and salt to a pan and place over medium heat. Stir to combine and make a caramel. Add the walnuts in at the end.
- Transfer mixture to round cake pan.
For the crumble
- In a processor, combine the brown sugar, flour, butter, cinnamon and salt. Pulse until the mixture resembles coarse breadcrumbs. Set aside.
For the cake
- Whisk together the buttermilk, sunflower oil and the eggs in a small bowl.
- Sift the flour, baking powder, baking soda and salt in another bowl.
- Beat the butter and sugar in a mixer until light and fluffy. Add the buttermilk mixture and the flour mixture, alternating between the two. Beat well, every time you make an addition, until all of the ingredients are completely incorporated.
- Pour half of the batter over the caramel in the cake pan. Sprinkle with half the crumble mixture. Carefully spread the rest of the batter and top off with the remaining crumble.
- Bake for 50-60 minutes or until you insert a toothpick into the cake and it comes out clean.
- Let the cake cool on a wire rack. Use a knife to loosen the cake from the perimeter of the pan, to make it easier to remove. Overturn onto a serving platter while still warm. Allow to cool before slicing.