Place the apple cider in a small saucepan and bring to a boil. Reduce the heat and simmer until the cider reduces to ½ cup. Remove from heat and set aside to cool down.
Preheat oven to 350°F. Lightly grease 2 (6-count) donut pans with non-stick spray.
In a medium bowl, whisk together flour, baking powder, salt, cinnamon, nutmeg, and allspice. Set aside.
In a medium bowl, using an electric mixer, cream butter and sugar until light and fluffy. About 3 minutes. Add eggs, one at a time and vanilla. Beat until incorporated.
Add flour mixture and reduced apple cider alternately ending the process with flour mixture. Continue mixing until well incorporated. Scrape the bowl as needed. Add sour cream, mix until well combined.
Spoon the batter into the prepared pans. Fill them ¾ of the way. Bake for 15 minutes or until golden brown. Remove from oven and allow the donuts to cool down for 5 minutes. Remove from pan.
While the donuts are baking, mix light brown sugar with granulated sugar and cinnamon. Set aside. Prepare the icing by mixing powdered sugar with 4 tablespoons of apple cider.
While the donuts are still warm, coat them with the sugar-cinnamon mixture or ice them with apple cider icing. Serve warm.