Apple Cider Donut Cake

Instructions

1. Preheat the oven to 350ºF (175°C) and set an oven rack in the middle position. Butter or coat an 8-inch (20-cm) square metal baking pan (see note) with nonstick spray. Line the pan with an 8x16-inch (20x38-cm) piece of parchment paper, leaving a 2-inch (5-cm) 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.
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 (120 ml), 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 (80 ml) and leave the remaining reduced cider in the skillet.
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 (80 ml) of reduced cider. Whisk until evenly combined. Add the flour, baking powder, and baking soda, and whisk until smooth.
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.
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.
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.