Preheat the oven to 350F (180C). Butter and dust with oat flour a 9 or 10-inch (23-25cm) Bundt pan.
In a medium bowl, whisk oat flour, cocoa powder, salt and baking powder. Set aside.
In another bowl add honey, butter and vegetable oil.
Mix until creamy.
Incorporate eggs one at a time. Add vanilla extract and mix to combine.
With the mixer on low, gradually incorporate the oat flour mixture.
Alternate with the buttermilk.
Mix until all is well incorporated.
Pour the batter into the prepared pan.
Bake for about 50-60 minutes or until a toothpick inserted into the center comes out clean. If browns too fast, you can cover it with aluminum foil and continue baking.
Allow to cool slightly in the pan onto a rack for about 10 minutes.
Invert onto a serving platter.