Preheat oven to 350°F and line two baking sheets with parchment paper.
In a medium bowl, combine flour, salt, baking soda, and cinnamon (if using). Set aside.
In the bowl of a standing mixer with the paddle attachment or a handheld mixer, combine butter and both sugars, mixing until light and fluffy, around 2 minutes.
Add in the egg and vanilla extract, and mix until combined.
Mix in the dry ingredients (flour, salt, baking soda, and cinnamon) until combined. Do not over-mix! Fold in chocolate chips (if using).
Add the cornflakes to a small bowl and use your hands to just slightly crush them, but not too much. There should still be some bigger pieces in the bowl.
Use a cookie scoop or your hands to form 1.5 tbsp sized balls of dough. Roll each ball in the bowl of corn flakes until they are generously covered. Place the dough onto the baking sheets, around 3-4 inches apart and bake one sheet at a time, for 8-11 minutes. The edges will be set but the middles still look soft.
Let the cookies cool on the baking sheet for 10 minutes, then transfer to a wire rack to cool completely.