Preheat the oven: Set the oven to 350°F (175°C) and line a loaf pan with parchment paper, leaving some overhang on the sides for easy removal later.
Reduce the apple cider: In a small saucepan, simmer 1½ cups apple cider over medium heat for 15–20 minutes until it reduces to about ¾ cup and slightly thickens. Let it cool slightly before using.
Make the cinnamon sugar: In a small bowl, mix together the ¼ cup white sugar and ½ teaspoon cinnamon until evenly combined. Set aside.
Mix the dry ingredients: In a large bowl, whisk together the flour, cinnamon, nutmeg, cardamom, baking soda, baking powder, and salt until evenly combined.
Mix the wet ingredients: In a separate bowl, whisk together both sugars, eggs, oil, reduced apple cider, applesauce, and vanilla extract until smooth.
Combine the batter: Pour the wet ingredients into the dry ingredients and whisk until just combined — stop as soon as you no longer see streaks of flour.
Pour and top: Pour the batter into the lined loaf pan, spreading it evenly. Sprinkle half of the cinnamon sugar mixture evenly over the top.
Bake: Transfer the loaf pan to the oven and bake for 45 to 55 minutes, or until a toothpick inserted in the center comes out clean.
Finish with cinnamon sugar: Let the loaf cool for about 10 minutes, then lift it out of the pan and place it on a wire rack. Brush the top with melted butter and sprinkle the remaining cinnamon sugar evenly so it sticks beautifully.
Slice and serve: Once fully cooled, cut into thick slices and enjoy!