Pour the apple cider into a small saucepan. Bring it to a boil over high heat. Once it's boiling, lower the heat to medium-low and simmer the cider until it's reduced to about 1/2 cup. This will take about 15 minutes. Once it's reduced, transfer the cider to a heat-proof bowl or container to cool.

Preheat the oven to 350°F and coat the inside of a 9x5” loaf pan with nonstick cooking spray.

Whisk the flour, baking powder, baking soda, and cinnamon in a medium bowl.

Cream the butter and 1 cup of brown sugar with an electric mixer in a large mixing bowl. Beat the mixture at medium speed for about two minutes or until it's light and fluffy. Beat in the eggs, vanilla, and apple cider.

Adjust the mixer speed to low and alternate between adding the flour mixture and the milk. Do this in a few batches - alternating between the two will ensure the batter is not overmixed.

Transfer the batter to the prepared loaf pan and smooth the top.

In a small bowl, combine the remaining ¼ cup of brown sugar and ½ teaspoon cinnamon. Sprinkle the mixture over the top of the loaf.  

Bake the loaf for 50 to 55 minutes, or until a toothpick inserted into the center comes out clean.

Allow the loaf to cool in the pan for 10 minutes, then turn it out onto a wire rack to cool completely.