In a small bowl, combine eggnog and vinegar. Set aside.
In a large bowl, combine flour, brown sugar, baking powder, pumpkin pie spice, salt, and baking soda. Blend well.
Using a grater, grate the cold butter into the flour mixture. Fold butter into flour mixture until well-blended.
In a medium bowl, combine the eggnog mixture, egg, and sweet potatoes. Whisk until well-blended.
Add the sweet potato mixture to the flour, along with the cinnamon chips and pecans.
Mix altogether until just combined.
Turn onto a lightly floured surface, and knead 10-12 times. Gently form dough into a large ball.
Place the dough onto a well-greased baking sheet and flatten into a circle about 10-inches in diameter, and about 3/4-inch thick.
Brush the dough lightly with eggnog and sprinkle evenly with coarse sugar.
Using a long knife, cut into 8 wedges.
Carefully separate wedges on baking sheet, pulling them just slightly apart.
Bake at 400 degrees for 16-20 minutes, or until edges are golden brown.
Cool slightly, and serve!