Wash and dry potatoes and pierce around sides with fork. Place in center of microwave and cook on high for approximately 4 minutes, or until yielding when squeezed and soft and fluffy inside. Cut in half, and allow to cool to room temperature.
Using a tablespoon, scoop pulp of potato and place in blend, discarding skins. Add eggs, Greek yogurt and ¼ cup of the milk and blend until smooth. Next, pulse in vanilla, cinnamon, ginger, nutmeg, cardamom, cloves, and white pepper until just combined.
In small bowl, mix together baking soda, salt, white pepper, and protein powder. Pulse this mixture into the blender in batches until smooth, adding the additional milk if batter seems to thick.
Prepare 9” x 9” rimmed baking pan with cooking spray. Pour in batter and bake for approximately 14 to 16 minutes or until turning lightly golden brown and toothpick pulls clean from the center. Let cool for 30 minutes and cut into 8 bars.
Dust with additional cinnamon and a bit of powdered sugar, if desired.