Preheat oven to 350 F. Line cupcake pans with paper liners.
In a large bowl, whisk together flour, baking powder, baking soda, cinnamon and salt. Set aside.
In a second large bowl, beat sugar and oil together with an electric mixer until well combined, about 30 seconds. Add applesauce, condensed milk and vanilla, beat for 30 seconds, then add eggs one at a time, beating well after each addition. Add flour mixture in three parts, alternating with the buttermilk, and continuing to beat until well combined.
Pour batter into prepared muffin tin.
Bake until golden brown and a toothpick inserted in the middle of each cake comes out clean, about 25-30 minutes.
Set aside to let cool for 10 minutes.
For the frosting, put sugar, butter, cider, cinnamon and salt into a large bowl and beat with an electric mixer until light and fluffy, about 5 minutes. Frost and serve!