Beat butter and shortening together until well-combined.
½ cup salted butter, ½ cup shortening
Mix in sugar until incorporated.
1 ½ cups granulated sugar
Add eggs and vanilla, and mix in until combined.
2 large eggs, 1 teaspoon vanilla extract
Stir in flour, cream of tartar, baking soda, and salt until just combined.
2 ¾ cups all-purpose flour, 1 teaspoon cream of tartar, 1 teaspoon baking soda, ¼ teaspoon salt
Cover, and chill dough for at least 1 hour.
Preheat oven to 375 F. Line baking sheets with parchment paper or silicone baking mats.
Stir together sugar and cinnamon in a small, shallow dish.
⅓ cup granulated sugar, 1 ½ teaspoons ground cinnamon
Using a 1 ½ tablespoon cookie scoop, scoop out balls of cookie dough.
Roll into balls, and then roll in cinnamon/sugar.
Place on cookie sheet, and barely flatten cookies.
Bake for 8-9 minutes. Cookies will be set but still look wet between the cracks.
Let cool on baking sheet.
Notes
Butter: I use salted butter. If using unsalted butter, increase the salt to 1/2 teaspoon.
Shortening: The shortening helps to make the cookies soft and helps them to keep their shape.
All-purpose flour: It's important to properly measure the flour. You can weigh the flour (click on "metric" for the weights) or sift/stir the flour to break it up. Lightly spoon the flour into the measuring cup and level. Avoid packing the flour.