In a large mixing bowl, cream butter, brown sugar, and granulated sugar until smooth and creamy.
Add eggs one at a time, mixing after each addition. Stir in vanilla. Scrape down the bowl.
In a separate bowl, whisk flour, baking soda, cornstarch, cinnamon, and salt.
Add dry ingredients to wet ingredients and mix just until combined.
Cover and chill dough for 30–60 minutes.
Preheat oven to 350°F. Line baking sheets with parchment paper.
Mix cinnamon-sugar coating in a small bowl.
Scoop dough into 1½-tablespoon balls. Roll each ball in cinnamon-sugar.
Place on baking sheet, spacing cookies 2 inches apart.
Bake 9–11 minutes, until edges are set and lightly golden. Centers will look soft.
Cool 5 minutes on baking sheet, then move to a wire rack to cool completely. Add a pinch of flaky sea salt while warm if desired.