Place first three ingredients in a small pot and heat to boiling over medium heat. Continue boiling until the cider is reduced to about 3/4 cup. It will still look super-liquidy. That’s ok, it’s because it’s still warm. Let cool completely, and it will be a beautiful syrup.
Preheat oven to 350°F. Grease (and flour, if you are so inclined) a bundt cake pan or a tube pan. Mix together spice cake mix, melted butter, apple cider, and eggs until everything is incorporated and smooth.
Pour into bundt pan.
Bake for approximately 40 minutes, or until cake springs back when lightly touched.
Cool at least 10 minutes on a rack, then remove from cake pan.
With a mixer, cream together remaining stick of butter and cream cheese.
Add powdered sugar and mix until incorporated.
While continuing to mix, slowly add apple cider syrup until the frosting is pourable. This could take anywhere from 1/2 cup to 3/4 cup.
Pour frosting on top of cooled cake. Enjoy.
Recipe by Whitney Donohue at http://whitneydonohue.com/apple-cider-cake-with-apple-cider-frosting/