Cream the butter and sugars together.
Mix in the egg and vanilla.
Fold in the flour, baking soda, salt, and cinnamon until almost combined, then add the cinnamon crumbs and continue folding until there are no more streaks of flour.
Scoop the dough with a regular sized cookie scoop (2 tablespoons) and place them on a lined baking tray.
Sprinkle the tops with some of the leftover cinnamon crumbs, then place the tray in the freezer to freeze solid, about 20-30 minutes.
Increase the oven temperature to 350F/180C and bake the cookies for 10-11 minutes, or until the edges are golden brown but the middle is still pale.
Immediately out of the oven, sprinkle the tops with the last of the cinnamon crumb.
Let cool completely.
Whisk the vanilla, milk, and powdered sugar together until you get a semi-thick glaze.
Drizzle the cooled cookies with the glaze and enjoy!