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1
Preheat the oven to 350u00b0F.
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2
Spray an 8-inch cast-iron skillet with nonstick cooking spray.
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3
Pro tip: Place the softened butter, granulated sugar, and vanilla extract into a large bowl. Use a mixer to cream together on medium speed for 1 minute, or until pale and fluffy. Add the egg and continue to beat on medium speed for 30 seconds to one minute, until light and fluffy.
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4
Add the flour, cinnamon, corn starch, baking soda, cream of tartar, and salt to the bowl. Beat the mixture on medium speed for about 1 minute, until all ingredients are combined. Scrape down the sides of the bowl with a rubber spatula, as needed.
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5
Place the granulated sugar, cinnamon, and a pinch of salt in a small bowl. Mix with a fork to combine.
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6
Transfer the cookie dough into the cast-iron skillet. Use a spoon or clean hands to press the dough into an even layer. Sprinkle the cinnamon sugar evenly over the dough.
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7
Bake the cookie for 28-30 minutes on the middle rack of oven, until golden-brown at the edges and a toothpick inserted in the center comes out clean.
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8
Check to see that the cookie is done. Remove from oven or add time as needed.
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9
Allow the cookie to cool for 10 minutes before serving.
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10
Serve the cookie warm directly from the skillet. Alternatively, the cookie may be cooled to room temperature in the skillet, then cut into slices.
