Heat oven to 375° F. Line a 12-cup muffin tin with liners.
In a large bowl, whisk together the coconut oil, honey, eggs, and buttermilk. In a medium bowl, whisk together the flours, baking powder, baking soda, salt, cinnamon and nutmeg.
Pour the flour mix into the wet ingredients and stir well to combine. Gently stir in the blackberries.
Divide the batter equally between the muffin cups and place in the oven. Bake for 20-25 minutes, until a tester inserted in a muffin comes out clean and the tops are slightly firm. Remove from oven and let cool in pan 5 minutes, then turn out onto a wire rack to cool 10-15 minutes more.
Muffins will keep, in a tightly sealed container in the fridge, for up to 5 days.