Preheat Oven: Set oven to 350°F (175°C). Line a baking sheet with parchment paper. Make the Dough: Cream butter and brown sugar until fluffy. Beat in egg, maple syrup, and vanilla. In a separate bowl, whisk flour, baking soda, salt, and cinnamon. Gradually mix into the wet ingredients. Bake: Drop rounded tablespoons of dough onto the baking sheet. Bake for 10-12 minutes or until golden. Let cool. Prepare the Icing: Whisk powdered sugar, maple syrup, vanilla, and milk until smooth. Glaze & Set: Drizzle or spread icing over cooled cookies. Let set before serving.