For both cinnamon mixtures, mix (in separate bowls) well, set aside.
For cookie dough, combine shortening and dark brown sugar in large bowl.
Beat til well blended.
Beat in eggs and vanilla til very well blended.
Combine flour, baking powder, salt and cinnamon in small bowl.
Add to creamed mixture, mix well.
Turn dough onto sheet of waxed paper and spread/pat out to a 9x7" rectangle.
Sprinkle evenly with Inside cinnamon mixture.
Roll up jelly-roll style into a log.
Dust all sides with Outside cinnamon mixture.
Wrap tightly with plastic wrap.
Refrigerate 4 hours or overnight.
Heat oven to 375º, spray cookie sheets with butter-flavored cooking spray.
Cut cold log into about 1/4" slices. It's ok if you can't slice that thin.
Bake for 8 minutes or til lightly browned on top.
Cool on cookie sheets for 4 minutes.
Then remove from cookie sheets, and cool the rest of the way on wire racks.
When cool, mix glaze ingredients well using as much or little milk as needed for a thick yet pipeable consistency.
Pipe glaze over each cookie.
Be careful when rolling this dough. If it starts to crack, smooth them. Roll slowly.
Also, I found it easier when you slice them, let the slice rest on the knife when moving them to the cookie sheet. If they fall apart a bit, don't fret, just push them back together! They bake up just fine!