Reduce the Apple Cider: In a small saucepan over medium heat, bring 1.5 cups of unfiltered apple cider to a gentle simmer. Cook for 15 to 18 minutes, swirling occasionally, until the liquid reduces down to exactly 1/3 cup of thick, aromatic cider concentrate. Remove from heat and allow to cool completely to room temperature (about 15 minutes).

Whisk Dry Ingredients: In a medium mixing bowl, whisk together the all-purpose flour, baking soda, cream of tartar, ground cinnamon, nutmeg, and sea salt. Set aside.

Cream Butter and Sugars: In a large stand mixer bowl fitted with the paddle attachment (or using a hand mixer), beat the softened butter, granulated sugar, and dark brown sugar together on medium-high speed for 2 to 3 minutes until light, fluffy, and pale in color.

Add Wet Ingredients & Cider Reduction: Beat in the room temperature egg and vanilla extract until fully incorporated. Pour in the cooled 1/3 cup reduced apple cider and mix on low speed just until combined (the batter may look slightly curdled for a second due to the cider acidity, which is completely normal).

Combine & Chill the Dough: With the mixer on low speed, gradually add the dry flour mixture in two batches, mixing just until soft dough forms and no flour pockets remain. Do not overmix! Cover the bowl with plastic wrap and chill in the refrigerator for at least 30 minutes (this firms the dough and deepens the apple spice flavor).

Roll in Cinnamon Sugar & Bake: Preheat your oven to 350°F (175°C) and line two large baking sheets with parchment paper. In a small bowl, stir together 1/4 cup sugar and 1 tsp cinnamon. Using a 2-tablespoon cookie scoop, scoop dough balls, roll between your palms, and roll generously in the cinnamon sugar mixture. Place 2 inches apart on the prepared sheets. Bake for 10 to 12 minutes until edges are set and tops are puffed and crackled (centers will still be very soft). Let cool on the baking sheet for 5 minutes, then transfer to a wire rack.

Make Salted Caramel Glaze & Drizzle: In a small saucepan over medium heat, melt brown sugar, butter, and heavy cream together until boiling, stirring constantly for 1 minute. Remove from heat, whisk in sifted powdered sugar until glossy and smooth. Drizzle generously over cooled cookies with a spoon or fork, and finish with a delicate pinch of flaky sea salt. Let glaze set for 10 minutes, then enjoy!