Preheat oven to 375°F.: The moment you feel the warm, dry heat from a preheated oven, you know it's ready, and consistent oven temperature is critical for even rise and cracking on top. When you preheat fully, the first contact of the dough with the hot tray starts the leavening reaction immediately, producing those signature cracks. A common mistake is underpreheating, which leads to flat, greasy cookies, so allow the oven to reach temperature before baking and use an oven thermometer if you suspect inaccurate heat.
In a large mixing bowl, cream the shortening, sugar and eggs until creamy. Sift the flour, cream of tartar, soda and salt into the sugar mixture and whisk to combine. Use a wooden spoon to mix in the white chocolate chips.: As you beat, listen for the change in texture from gritty to smooth, and watch as the mixture lightens slightly and becomes glossy, which tells you air has been incorporated for lift. Proper creaming dissolves sugar into fat and eggs, creating a stable base for the flour to join. If you skip thorough creaming you'll have dense cookies, so take the time to beat until smooth and unified, stopping to scrape the bowl so no pockets of shortening remain.
In a small bowl, whisk the sugar with the cinnamon. Use a #24 scoop or 2 tablespoon scoops to portion the dough and roll into balls. Dip each ball into the cinnamon sugar mixture and place 6 dough balls on a lightly greased or parchment prepared cookie sheet.: When you sift and whisk, the dry blend becomes airy and uniform, preventing lumps and ensuring even distribution of the leavening agents so every cookie responds the same during baking. The smell is neutral at this point, but the texture of the dough will start to thicken as the flour hydrates. Overmixing here will develop gluten and toughen the cookies, so fold until just combined.
Bake for 9-12 minutes or until cookies rise and crack on top. The cookies won't brown so be careful not to over bake. Allow the cookies to cool on the sheet for 10 minutes then transfer to a cooling rack. Store the cookies in an airtight container for up to 3 days.: Stirring by hand with a wooden spoon lets you feel the dough s consistency and ensures the white chocolate chips are distributed without breaking them. You will notice the chips dotting the dough like tiny islands, promising melty bites after baking. A common issue is overworking the dough so the chips break or melt into the mix; fold gently until they are evenly scattered.
In a small bowl, whisk the sugar with the cinnamon.: The scent of cinnamon will bloom as you whisk, creating an inviting aroma that hints at the cookies to come. This coating provides a sweet, slightly crunchy contrast to the tender cookie inside. Make sure the cinnamon is evenly blended with the sugar so each ball gets consistent flavor; clumps of cinnamon will create uneven pockets of spice.
Use a #24 scoop or 2 tablespoon scoops to portion the dough and roll into balls.: When you portion with a scoop you get uniform cookies that bake evenly, and the dough should feel slightly tacky but hold shape when rolled into a ball. Rolling warms the surface slightly, which helps the coating adhere. If you scoop unevenly, some cookies will overbake while others remain underdone, so be consistent with scoop size.
Dip each ball into the cinnamon sugar mixture and place 6 dough balls on a lightly greased or parchment prepared cookie sheet.: As you roll in the coating you will notice the sugar sticking and forming a glistening shell, and placing space between the balls allows them to spread into round, cracked tops. Using parchment prevents sticking and browning on the bottom. Crowding the sheet leads to merged cookies, so leave ample space and bake in batches if needed.
Bake for 9 to 12 minutes or until cookies rise and crack on top.: Watch for the telltale cracked surface; the cookies will still be pale but set at the edges, and you may smell a sweet, cinnamon note as they finish. Because these cookies do not brown much, resist the urge to bake until golden or they will dry out. Overbaking is the most common mistake here, so check at the lower end of the time range and trust the cracks and slight firmness at the edge rather than color.
Allow the cookies to cool on the sheet for 10 minutes then transfer to a cooling rack.: Cooling on the sheet lets the centers finish setting while the bottoms relax, and moving them too soon can cause them to break apart. After a brief rest they will lift easily and continue to firm on the rack, maintaining a tender interior. A mistake is immediately stacking warm cookies which traps steam and makes them soggy, so give them that resting period.
Store the cookies in an airtight container for up to 3 days.: Proper storage preserves texture, keeping the cookies soft while preventing the white chocolate chips from becoming chalky. Place a small piece of parchment between layers to avoid sticking. Leaving them exposed will dry them out quickly, so an airtight container is essential for freshness.