• Preheat oven to 350 degrees F.  Grease 13 x 9 x 2-inch pan or spray with non-stick spray. If desired fit pan with a parchment or foil sling and spray that too. (helps with easy removal and cutting of bars once cool)
• Whisk together flour, cream of tartar, baking soda and salt in small bowl.
• Cream together butter and sugar in large mixing bowl until fluffy and lighter in color. I use a hand or stand mixer and cream for several minutes.  Add vanilla and eggs, one at a time, and mix until combined.
• Gradually add in flour mixture.
• Stir in the cinnamon chips.
• Spread two-thirds of the cookie dough in prepared pan. I find it easiest to do this with a greased spatula or greased fingers as the dough is sticky. Then sprinkle with cinnamon sugar. Add the rest of the dough in dollops on top of the cinnamon sugar
• Bake for about 25-30 minutes or until set and slightly golden brown.
• Cool about 10 minutes in pan on wire rack.

Glaze:

• While bars are cooling, whisk together powdered sugar, vanilla and 1 tablespoon milk. Add more milk to reach desired texture.
• Drizzle glaze over still warm bars. Cool completely in pan. (If using sling, lift cooled bars to cutting board) and cut into 24 squares.