Preheat oven to 400 degrees F. Line or grease 24 muffin cups.
Combine butter and yogurt with electric mixer until completely combined. Mix in sugars and beat until fluffy. Add vanilla and pumpkin and mix until well combined. Add eggs and mix until well combined.
In a separate bowl, combine white whole wheat flour, baking soda, baking powder and salt. Slowly mix into the wet ingredients.
Divide batter equally into two bowls.
Into one bowl add cocoa powder and buttermilk, and mix just until combined.
In the other bowl, add cinnamon and pumpkin pie spice.
Scoop a bit of each batter into each muffin cup (totaling about 2/3 of the way full with both batters combined). If desired use a knife to swirl together the chocolate and pumpkin.
Bake for 15-17 minutes, or until a knife inserted into the center of a muffin comes out clean.
Remove from oven and allow to cool.
These freeze great for quick weekday breakfasts. I let mine cool completely, wrap in plastic wrap then place into a freezer bag.