Preheat the oven to 338F/170C.

Combine chopped pecans, white and brown sugar, melted butter, cinnamon and salt in a mixing bowl and mix until well combined. The pecans and sugar should be well coated with the melted butter and cinnamon.Set aside while you make the cake.

Cream the butter and sugar together (a stand mixer or hand mixer is handy for this step). They should be light, fluffy and pale in color.

Now add the sourdough starter, flax, buttermilk and vanilla to the butter and sugar and mix until well combined. Set aside while you assemble the dry ingredients.

In a separate bowl, add the flour, baking powder and salt. Mix until well combined.

Now, add the dry ingredients to the wet ingredients in 3 to 4 small batches, folding them in gently.

Take a cake pan that has been well greased with plenty of butter. Pour half of the cake batter into the pan.

Top the cake batter with half of the streusel topping and then add the remainder of the cake batter.

Top the cake with the remainder of the pecan and cinnamon streusel mixture. Don't worry if it doesn't completely cover the top, the cake will fill in the gaps.

Bake the cake in the oven at 338F/170C for around 45 minutes or until a skewer comes out clean (I have baked this in a fan forced oven - just don't make the oven too hot or the topping on the cake will burn).

Allow the cake to cool in the tin for around 10 to 15 minutes. You can then pop it onto a wire rack to cool completely.