Heat the oven at 180°C/356°F.
Beat the eggs in a big bowl, then add lemon juice, buttermilk, sugar and coconut oil.
Add gradually the flours, baking powder, baking soda, cinnamon and walnuts, mixing well until a sticky mixture is formed.
Grease a bundt cake tin with coconut oil and pour the mixture into the tin.
Bake for 50 minutes, then remove from the oven and set aside to cool for five minutes before removing from the tin.
When the cake is completely cool, wrap in plastic foil and refrigerate.
For the vegan sauce, place all the ingredients (except the coconut oil) in a blender and process to obtain a smooth liquid.
Transfer the mixture in a sauce pan over low heat and stir continuous until it starts simmering.
Turn off the heat, whisk in the coconut oil and set aside to cool. Keep in the refrigerator in an airtight container.
Before serving, bath the bundt cake in chocolate sauce and decorate with blackberries.