How to Make It
Prepare the Toasted Cinnamon Toast Crunch: Preheat oven to 275°F. Toss cereal, melted butter, and cinnamon together on a baking sheet lined with parchment paper. Bake in preheated oven until toasted and golden brown, about 15 minutes. Let cool on baking sheet until hardened, about 30 minutes.
Prepare the Cinnamon Toast Crunch Sugar Coating: Place cereal in a large ziplock plastic bag. Using a rolling pin, or anything flat and heavy, crush cereal until finely ground. Pour into a small bowl. Add sugar and cinnamon, stirring to combine. Set aside.
Prepare the Dough: Preheat oven to 425°F. Whisk together flour, cream of tartar, cinnamon, and baking soda. Set aside. Beat butter and cream cheese in bowl of a heavy-duty stand mixer fitted with a paddle attachment on low speed until creamy, about 1 minute. Add granulated sugar and brown sugar, and beat until smooth, 1 to 2 minutes. Add egg and vanilla, beating to incorporate. Gradually, add flour mixture to butter mixture, beating on low speed just until incorporated, 1 to 2 minutes, stopping to scrape sides of bowl as needed. Add Toasted Cinnamon Toast Crunch, beating on low, until incorporated evenly into dough, 15 to 30 seconds.
Using a 2-inch (#24 scoop, about 1 1/3 oz.) cookie scoop, measure out about 20 dough balls. Toss 1 ball at a time in Cinnamon Toast Crunch Sugar Coating, being careful not to flatten dough. Repeat with remaining balls. Arrange coated dough balls about 3 inches apart on 3 baking sheets lined with parchment paper.
Bake in preheated oven until slightly golden but centers are still gooey, about 6 minutes. Let cool on baking sheets on a wire rack, 10 minutes. Transfer cookies directly to wire racks to cool completely, about 20 minutes.