Preheat oven to 375 degrees F
In a large mixing bowl, sift the chestnut flour. Add the orange zest, pinch of salt, and coconut flour.
Mix well and then gently add the water, egg, agave syrup, orange juice, and vanilla.
Fold in the frozen berries, nuts, and coconut oil until there are no lumps and everything is well combined.
Lightly oil an 8-inch cake pan. Pour cake mixture into the pan.
Bake for 40 minutes. Remove from pan and let cool.
Dust with powdered sugar. Serve and enjoy!