Reduce the Cider: In a small saucepan over medium heat, simmer 2 cups of fresh unfiltered apple cider for 15-20 minutes until reduced down to exactly 1/2 cup of rich, dark amber concentrate. Pour into a heatproof bowl and set aside to cool. Reserve 3 tablespoons of this reduced syrup for the glaze.

Brown the Butter: In a light-colored saucepan over medium heat, melt the unsalted butter. Swirl the pan occasionally as the butter foams and crackles. After 4-5 minutes, nutty golden brown flecks will form at the bottom. Immediately remove from heat and pour into a mixing bowl to cool for 10 minutes.

Mix the Dough: Whisk the granulated sugar and dark brown sugar into the cooled browned butter until combined. Whisk in the egg, vanilla extract, and remaining cooled reduced cider (about 5 tablespoons). In a separate bowl, whisk together the flour, baking powder, baking soda, ground cinnamon, nutmeg, allspice, and sea salt. Fold dry ingredients into wet ingredients with a rubber spatula just until combined. Chill dough in the refrigerator for 30 minutes.

Bake to Soft Perfection: Preheat oven to 350°F (175°C) and line two large baking sheets with parchment paper. Use a 2-tablespoon cookie scoop to drop mounds of dough onto sheets, spaced 2 inches apart. Bake for 10-12 minutes until edges are lightly golden and set, but centers remain soft and puffed. Let rest on pan for 5 minutes, then transfer to a wire cooling rack.

Glaze & Set: In a small bowl, whisk together powdered sugar, reserved 3 tablespoons reduced apple cider, melted butter, and ground cinnamon until a smooth, thick glaze forms. Generously drizzle or spoon over warm cookies. Allow glaze to set for 15 minutes before serving.