Preheat oven to 400 degrees F.

Combine butter, Greek yogurt, sugar, eggs, vanilla and pumpkin in a bowl and mix well to combine. In a separate bowl, mix together flours, cocoa powder, baking soda and salt. Combine wet and dry ingredients, add in milk and stir until well combined. Scoop into a muffin pan that has been lightly sprayed with cooking spray or is lined with muffin liners.

Place muffins in the oven and immediately reduce the temperature to 350 degrees F. Bake for 15-20 minutes or until tops spring back when touched. Remove from oven and allow to cool. Store covered, preferably in the refrigerator. Muffins can also be frozen.