Preheat the oven to 375 degrees F (190 degrees C). Line a baking pan with parchment paper or spray with non-stick coating spray.
In a large bowl, cream together the softened butter and the sugar until fluffy. Add eggs one at a time, mixing after each. Add the vanilla.
In a medium bowl, sift together the flour, baking soda, cream of tartar, cinnamon and salt. Stir dry mixture into the creamed sugar mixture until blended. Do not overmix.
In a small bowl, mix ¼ cup granulated sugar with 1 teaspoon cinnamon in a small bowl. Form dough into 1.5" diameter balls and roll in cinnamon-sugar topping.
Place cookies on baking pan and bake in oven for 8-10 minutes or until cookies start to crack on top. Do not over cook or your cookies will not be soft!
Store cookies in an airtight container for 5 days or freeze up to 2 months.
Recipe by CHIC AND SUGAR at https://www.chicandsugar.com/2014/11/holiday-cookie-1-snickerdoodle/