Preheat oven to 375°F (190°C) and line baking sheets with parchment paper.

In a medium bowl, whisk together flour, cream of tartar, baking soda, and salt.

In a large bowl, cream together butter and granulated sugar until light and fluffy.

Beat in eggs one at a time, then stir in vanilla extract.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Divide the dough into three equal portions for each snickerdoodle type.

For Classic Snickerdoodles, combine 1/4 cup granulated sugar and 2 teaspoons ground cinnamon in a small bowl.

For Chocolate Chip Snickerdoodles, fold 1 cup mini chocolate chips into one portion of dough, then combine 1/4 cup granulated sugar and 2 teaspoons ground cinnamon in a small bowl.

For Pumpkin Snickerdoodles, stir 1/2 cup pumpkin puree and 2 teaspoons pumpkin pie spice into the last portion of dough, then combine 1/4 cup granulated sugar and 2 teaspoons ground cinnamon in a small bowl.

Roll each dough portion into 1-inch balls, then roll each ball in its respective cinnamon-sugar mixture to coat evenly.

Place cookies 2 inches apart on the prepared baking sheets.

Bake for 10-12 minutes, or until the edges are set and the centers are still soft.

Let cookies cool on the baking sheets for a few minutes before transferring to a wire rack to cool completely.