First, cook the sweet potato. Prick it all over with a fork place it on a microwave safe plate. Microwave it for about 6 minutes, until it's soft and mashable. Allow it to cool enough to handle, then cut it in half. Scoop the filling right out of the skin into a bowl and mash it completely. Set the bowl aside to let the sweet potato finish cooling for another few minutes.

In the meantime combine the flour, brown sugar, baking powder, pumpkin pie spice and salt. Whisk them together to aerate them. Add the milk, egg yolks and vanilla to the bowl of cooled sweet potato. Whisk that mixture together until smooth. Pour those wet ingredients into the bowl of dry ingredients and whisk it all together until a smooth batter forms. Take the separated out egg whites and whip them up with a hand mixer until they are like clouds. Fold them into the batter. Cover the bowl and let it rest for at least 30 minutes in the refrigerator, or up to overnight.

Pre-heat an electric griddle to 325 or heat a large griddle pan over medium high heat when ready to cook the pancakes. Lightly grease the griddle with butter and ladle generous scoops of the batter on it. Let the pancakes cook for about 4 minutes, then flip them to cook on the other side. Keep cooking in batches as needed until the batter is gone.

While the pancakes cook, prepare the walnut honey butter. Simply combine the ingredients in a bowl and stir it together thoroughly. Serve the warm pancakes immediately with the honey butter and enjoy!