Reduce the Apple Cider: Pour 1 1/2 cups of fresh spiced apple cider into a small saucepan over medium heat. Simmer gently for 15 to 20 minutes until reduced down to exactly 1/2 cup of concentrated, fragrant apple cider syrup. Set aside to cool to room temperature.

Prep Bundt Pan & Dry Ingredients: Preheat your oven to 350°F (177°C). Generously grease a 10-to-12 cup bundt pan with baking spray with flour or melted butter coated in flour, tapping out excess. In a large bowl, whisk together the flour, baking powder, baking soda, ground cinnamon, nutmeg, allspice, and salt.

Cream Butter & Sugar: In a stand mixer fitted with the paddle attachment (or using a hand mixer), beat the softened butter, brown sugar, and granulated sugar on medium-high speed for 3 to 4 minutes until pale, light, and fluffy. Beat in the eggs one at a time, followed by the vanilla extract.

Alternate Wet & Dry: Whisk the cooled cider reduction and buttermilk together. With mixer on low speed, add the dry ingredients in three additions, alternating with the cider-buttermilk mixture in two additions, mixing just until combined. Do not overmix.

Bake to Golden Perfection: Spoon the thick batter evenly into the prepared bundt pan and smooth the top with a spatula. Bake for 48 to 55 minutes, or until a wooden skewer inserted into the thickest center comes out clean with a few moist crumbs. Let cool in the pan on a wire rack for 10 minutes, then invert onto the rack.

Apply Cinnamon Sugar Donut Crust: While the cake is still warm, generously brush the top, sides, and flutes with the melted butter using a silicone pastry brush. Immediately dust and spoon the cinnamon sugar mixture all over the cake, pressing gently so it sticks in a thick, sparkling donut-style shell. Cool slightly and slice warm.