Step 1

Preheat the oven to 350ºF and set an oven rack in the middle position. Butter or coat an 8-inch square metal baking pan (see note) with nonstick spray. Line the pan with an 8x16-inch piece of parchment paper, leaving a 2-inch overhang on two sides. You'll have to create seams in the corners and along the edges of the pan to get it to stay put.

Step 2

In a small skillet, bring the apple cider to a boil over medium heat. Gently boil until the cider is reduced to ½ cup, 10 to 15 minutes. (If you accidentally over-reduce it, make up the difference with more cider.) Let cool for about 10 minutes. Measure out ⅓ cup and leave the remaining reduced cider in the skillet.

Step 3

In a large bowl, whisk the sugar and eggs until pale and foamy, about 1 minute. Whisk in the sour cream, followed by the butter, and then the nutmeg, vanilla, salt, and the ⅓ cup of reduced cider. Whisk until evenly combined. Add the flour, baking powder, and baking soda and whisk until smooth.

Step 4

Pour the batter into the prepared pan and bake until the cake is puffed and golden and a skewer inserted into the center comes out clean, 30 to 35 minutes. Set the pan on a rack to cool for about 15 minutes then use the parchment paper to lift the cake out of the pan and set it on the rack to cool.

Step 5

Make the Glaze: To the skillet with the remaining reduced cider, add the butter, sugar, and salt. Bring to a boil over medium heat and gently boil until very thick, 30 to 60 seconds. Drizzle the warm cake evenly with the glaze. Let the glaze set for a few minutes while you make the cinnamon-sugar topping.

Step 6

In a small bowl, mix the cinnamon and sugar until evenly combined. Sprinkle a generous layer of the mixture evenly over the glazed cake, reserving a bit to add a fresh dusting before serving, if desired. Cut the cake into squares and serve.