Preheat oven to 350 degrees F. Line 24 muffin cups with paper liners.
In a large bowl, add cake mix, apple cider, eggs, and oil and beat with an electric mixer for about 2 minutes.
Fold in grated apples.
Scoop batter into muffin cups, filling each one about 2/3 full.
Bake for 20-24 minutes or until a toothpick inserted into the center of a cupcake comes out clean. Let cool in the pans for about 10 minutes, then remove cupcakes from pan and let cool completely.
While cupcakes cool, prepare frosting by mixing together softened butter and apple cider until completely combined. Add in powdered sugar and cinnamon and mix until smooth (add more or less powdered sugar, depending on how thick or thin you prefer your frosting).
Frost the top of each cupcake and sprinkle with cinnamon as a garnish if you prefer.