Skip making donuts and make my incredible Apple Cider Donut Cake instead — it's easier and packed full of that wonderful warm fall flavor you're looking for.
Preheat the oven to 350°F (180°C) and butter and flour a 12-cup capacity (2.84 liters) bundt cake pan. Set aside.
Pour the apple cider into a shallow saucepan and bring to a boil over medium heat until the cider is reduced to 1 cup (8floz/240ml).
Transfer the reduced cider to a glass measuring cup with a pour spout and add the cold milk. Set aside until the mixture has cooled to room temperature.
Once the cider mixture has cooled, make your batter: with a mixer or in a large bowl, whisk together the granulated sugar, brown sugar, eggs, oil, and vanilla extract until well blended.
Pour in the cider mixture and whisk until combined.
In a separate medium bowl, stir together the flour, baking powder, baking soda, salt, and nutmeg, and then add this to the wet ingredients in three increments. Stop stirring just as soon as everything is fully mixed.
Pour the batter into your prepared pan and bake for 35-45 minutes, or until a wooden skewer inserted into the cake comes out clean. Let cool in the pan for 10 minutes and then invert onto a wire rack.
Immediately coat the warm cake in cinnamon sugar and then let cool completely. Store leftovers in an airtight container at room temperature for up to three days.