In a small bowl, mix together all of the ingredients for the cinnamon pecan filling. Set aside.
In the bowl of a countertop mixer, add 4 tablespoon of the softened butter, sugar and salt. Mix on medium speed until light and fluffy (~2-3 minutes). (Note: The remaining butter will be used after the dough has risen.)
Add the egg and mix until just absorbed.
Add the milk, yeast and flour and mix for 1-2 minutes on low speed, or until a smooth dough forms.
Increase speed to medium and mix for 4 more minutes.
Cover dough and place in a warm location (85°F). Let rise for 11/2 hours.
Once risen, transfer dough onto a well-floured countertop. Roll into a 9”x12” rectangle.
Spread the remaining 4 tablespoon of softened butter evenly across the dough. Sprinkle with the Cinnamon Pecan Filling.
Beginning with a long edge of the dough, roll into a tight cylinder. Pinch seam closed. (Tip: Take care to keep ends of the cylinder even.)
Using a sharp knife, slice the cylinder into 12 pieces. (Each piece should be ~1” wide.)
Grease the bottom of an 8” cast iron skillet with butter. Place the rolls cut-side down into the skillet.
Cover skillet and refrigerate overnight.
The next morning, place skillet in a warm location until dough has filled bottom of the pan and increased in size (~75 minutes). (Note: Depending on how warm the spot is, this step may take a bit more or a bit less time.)
Bake at 325°F for 32-24 minutes, or until tops of rolls are golden brown.
Let buns cool in pan for 15 minutes.
While buns are cooling, make the glaze by whisking together the powdered sugar, milk and vanilla. Once buns have cooled slightly, drizzle with glaze.