Preheat the oven to 350ºF and grease the bottom and sides of a 9-inch cast-iron skillet with butter.
In a medium bowl, mix together flour, baking powder, and salt; set aside.
In the bowl of an electric mixer on medium speed, cream together the butter and sugar until pale and fluffy, about 3 minutes. Mix in egg. Reduce speed to low; gradually mix in flour mixture. Add in cinnamon chips.
Press the cookie dough into the prepared skillet.
Stir together cinnamon and remaining 1 tablespoon sugar in a small bowl. Sprinkle over the top of the dough. Bake for 20 minutes, until the edges are crisp and the center is set. Don't overbake. Serve warm sliced in to wedges.