Preheat oven to 350 degrees F.
Combine butter and yogurt with electric mixer until completely combined. Mix in sugar and beat until fluffy. Add eggs and mix until well combined. Add vanilla and pumpkin and mix until well combined. In a separate bowl, combine oat flour, cocoa powder, baking soda, baking powder and salt. Slowly mix into the wet ingredients. Add in buttermilk, and mix just until combined. If adding chocolate chips or nuts, fold in.
Scoop into a muffin pan lined with paper liners or sprayed with non-stick cooking spray
Bake for approximately 18-22 minutes or until a toothpick inserted into a muffin center comes out clean and muffins spring back when touched.
Remove from oven and allow to cool. Remove from pan and enjoy.