In a small saucepan over medium heat, simmer 1 1/2 cups unfiltered apple cider with the cinnamon stick for 12 to 15 minutes until reduced down to exactly 1/2 cup. Discard cinnamon stick and let cool to room temperature (reserve 2 tablespoons for the glaze).

Preheat oven to 350°F (175°C). Grease an 8.5x4.5-inch metal loaf pan and line with parchment paper, leaving an overhang on both sides for easy removal.

In a small bowl, mix the brown sugar, ground cinnamon, 1 tablespoon flour, and 1 tablespoon melted butter until crumbly; set aside.

In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, nutmeg, and sea salt.

In a large stand mixer bowl, beat softened butter, granulated sugar, and brown sugar on medium speed for 2 to 3 minutes until light and fluffy. Beat in eggs one at a time, followed by vanilla extract.

With mixer on low, alternate adding the dry flour mixture in two additions with the cooled cider reduction and sour cream, mixing just until combined. Gently fold in the diced Honeycrisp apples.

Spread half of the batter into the prepared loaf pan. Sprinkle 3/4 of the cinnamon swirl mixture evenly across the batter. Dollop remaining batter over top and smooth gently. Sprinkle remaining cinnamon sugar over top, then use a butter knife to gently swirl into figure-eight motions.

Bake for 50 to 55 minutes until a wooden toothpick inserted into the center comes out clean or with a few moist crumbs. (If browning quickly after 35 minutes, tent loosely with foil).

Cool in pan on a wire rack for 15 minutes, then lift out using parchment handles to cool completely.

Whisk confectioners sugar, warm apple cider, vanilla, and cinnamon until silky and pourable. Generously drizzle over the cooled loaf before slicing into thick slices.