Grease a 9” (23 cm) springform cake pan with a little coconut oil. Set aside.
Add chopped plums and coconut oil to a medium saucepan. Bring to a boil then lower the heat and simmer for 8 minutes. Let cool (this might take a while, but don’t place it in the fridge to speed up the process or the coconut oil will solidify).
In the meantime, toast the walnuts.
Preheat the oven to 350 °F / 175 °C.
Place walnuts on a baking sheet and bake for 8 – 10 minutes. Until golden and fragrant.
Place the walnuts in a food processor (or blender) and blend into a coarse flour consistency, some tiny walnut pieces are ok.
Combine whole wheat flour, ground walnuts, baking soda, baking powder, cinnamon, ginger and cardamom in a big bowl.
Once the plum-coconut oil mixture is at room temperature, mash the plums with a fork. Then add apple sauce, coconut nectar or maple syrup and vanilla extract. Stir to combine.
Add the wet mixture to the dry mixture and gently stir to combine.
Pour the cake batter into the prepared baking pan. Arrange the plum slices over the batter in large circles, gently pressing them into the batter. Brush the slices with a bit of coconut oil. Bake for 45 minutes or until you stick a knife and it comes out clean.
Allow the cake to cool down completely before slicing.
Enjoy this wholesome treat!