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1
Preheat the oven to 375 F. Grease 1 or 2 baking sheets and set aside.
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2
In a medium bowl, combine the flour, baking soda, cream of tartar, and salt.
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3
Set aside.
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4
Using a handheld mixer or stand mixer fitted with the flat beater attachment, beat the butter and 2 cups of the sugar on medium speed until fluffy, scraping the bowl once or twice while mixing.
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5
In a medium bowl, combine the eggs, milk, and vanilla.
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6
Slowly pour the liquid into the butter mixture while the mixer is running.
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7
Add the dry ingredients to the mixing bowl.
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8
Mix on low speed to incorporate the flour, scraping the bowl once or twice while mixing and stopping as soon as the dough is uniform.
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9
In a large, shallow bowl, combine the remaining 3 tablespoons sugar and the cinnamon.
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10
Separate the dough into 3 portions.
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11
Roll each portion into one large ball and roll the ball in the cinnamon mixture until it is completely covered.
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12
Place 1 ball of dough in the center of a baking sheet and, using the flat of your hand moistened with water, press down to flatten it into a 1/4-inch-thick by 10-inch-wide disk.
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13
Because you can bake only one cookie per baking sheet, you can speed the process by baking 2 cookies on 2 baking sheets at the same time.
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14
Bake each cookie for 20 to 24 minutes, until the cookie is soft and springy in the middle and crispy around the edges.
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15
Cool each cookie on the baking sheet for 5 minutes before carefully transferring it to a cooling rack with a spatula.
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16
Let cool completely.
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17
The cookies will keep in an airtight container at room temperature for up to 5 days.
