• Preheat oven to 350 degrees.
• In a large bowl, cream together butter, granulated sugar, and brown sugar using an electric mixer.
• Slowly add in egg, vanilla, salt, and baking soda. Beat until just combined. Slowly add in flour and mix well.
• In a separate small bowl, combine the 4 tablespoons of sugar and cinnamon.
• Scoop 2 tablespoons of dough and roll into ball. Roll in cinnamon sugar mixture and place on an ungreased cookie sheet. Repeat until dough runs out.
• Bake for 10-12 minutes. Cool completely before filling.

For Cinnamon Crème Filling:

• While cookies are baking, begin the crème filling.
• In a large bowl, beat butter on low speed for 30 seconds. Slowly add in powdered sugar one cup at a time, beating in between each cup.
• Once powdered sugar is incorporated, add in milk, vanilla, and cinnamon.
• Beat for 1 minute. If frosting is thick, add in 1 tablespoon of milk until desired consistency.
• Pipe 2 tablespoons of frosting between two cookies to make cookie sandwiches.