Cream room temperature butter and packed brown sugar together until light and fluffy. Add egg, vanilla extract, and real maple syrup, mixing smoothly.

In a separate bowl, whisk together flour, baking soda, cornstarch, and salt. Fold these dry ingredients into the butter mixture, being careful not to overmix.

Cover the dough and refrigerate for at least 1 hour, preferably overnight.

Preheat your oven to 350°F (175°C). Scoop chilled dough into balls and place evenly on a baking tray. Bake for 10–12 minutes.

Allow cookies to rest on the tray for 5 minutes before transferring to a wire rack to cool completely.

In a small bowl, whisk together powdered sugar, maple syrup, melted butter, and milk until smooth.

Spread glaze over cooled cookies and optionally sprinkle with flaky salt.