Preheat the oven to 175 degrees Celsius.
Line a oven safe baking pan with parchment paper.
Mix almond flour, coconut flour, baking soda and salt in a bowl.
Add egg, sugar, coconut oil, vanilla extract and tahini to a bowl or blender and mix/whish until you have a smooth mixture.
Add the dry ingredients to the wet and mix/whisk just until combined. The batter will be quite thick.
Fold in the chopped chocolate and blackberries.
Pour the batter to the lined baking pan nd bale in the oven for 18-23 minutes, just until the edges start to get golden brown (or longer if you prefer them more baked and less fudgy).
Take out of the oven and sprinkle with sea salt on top.
Let it cool completely before cutting it.