Cut butter into cubes, then freeze until ready to add it.
Use a prepared cast iron skillet or other desired pan. If using a pan other than cast iron, grease then flour the pan.
In a large mixing bowl, add the dry ingredients: flour, sugar, salt, baking powder, and baking soda.
Using a pastry cutter, cut butter into the flour mixture, it is ok to have smaller pieces of butter in the dougn.
In a mixing bowl, beat together the buttermilk, eggs, and vanilla.
Cut remaining butter into small pieces.
In a separate bowl, add remaining butter, brown sugar, and the cinnamon.
Melt the butter and sugar mixture in the microwave. Allow to cool slightly, then pour melted butter mixture gently onto a sheet of parchment paper and press and freeze.
Pour buttermilk mixture into flour mixture and stir until just combined.
Once chilled, cut the cinnamon butter into pieces and stir into the dough. This makes little cinnamon chips in the dough.
Transfer dough into pan or skillet, then bake for 23-25 minutes.