Line a baking sheet with parchment paper or a silpat and set aside.
In the bowl of a stand mixer, add the softened butter, brown sugar, and granulated sugar.
1 cup unsalted butter, 1 cup dark brown sugar, ¼ cup granulated sugar
Mix with paddle attachment on medium speed until fluffy and light in color, about 3-4 minutes. Stop the mixer and scrape the sides and bottom of the bowl.
Add the egg and vanilla extract and continue mixing on medium speed for another 2 minutes, stopping at least once to scrape down the sides and bottom of the bowl.
1 large egg, 1 ½ teaspoons vanilla extract
In a separate bowl, combine the flour, baking powder, baking soda, salt, and cinnamon, whisking to combine.
2 cups all-purpose flour, 1 teaspoon baking powder, 1 teaspoon baking soda, 1 teaspoon kosher salt, 1 teaspoon ground cinnamon
Add the dry ingredients to the mixer and stir on low until just combined. Stop the mixer and add in the crushed cereal. Stir on low until evenly combined. Do not overmix.
2 cups Cinnamon Toast Crunch Cereal
Using a ¼ cup (2 ounce) cookie or ice cream scoop, scoop out the dough and place on the baking sheet.
Gently press 3-4 pieces of Cinnamon Toast Crunch squares into the top of each cookie dough ball. Wrap the baking sheet with plastic wrap and place in the refrigerator for at least 12 hours.
Preheat the oven to 400˚F (200˚C) and line a second baking sheet with parchment paper or a silicone baking mat.
Remove the cookie dough from the refrigerator and divide cookie dough between the two baking sheets, spacing the cookie dough balls at least 3 inches apart (they may not all fit, bake in batches if necessary).
Bake for 14-16 minutes until the edges are just golden brown and the cookies are puffy.
Allow to cool on trays for 10 minutes, then transfer to a wire rack to cool completely. Bake rest of the cookies.