Preheat the oven to 180C/350F. Prepare 2 8-inch cake pans with cooking spray and parchment paper and set aside.
In a mixing bowl, add your flour, baking powder, baking soda, and cinnamon, and mix well. Set aside. In a separate mixing bowl, whisk together milk, vinegar, butter, sugar, and the applesauce, until combined and glossy. Let sit for 5 minutes. Combine your wet and dry ingredients.
Distribute the batter amongst the two baking pans. Bake for 25-30 minutes, or until a skewer comes out just clean.
Let the cakes cool in the pans for 10 minutes, before transferring to a wire rack to cool completely. Once cool, layer the cake by adding frosting between them and on top.
This makes a two layer cake. For a single layer cake, halve the ingredients and use just one cake pan.TO STORE: If you don't frost the cake, you can store the cake at room temperature. Keep it in a sealable container, with a paper towel on top. It will keep for 5 days. If you've frosted your cake, you must store it in the refrigerator. Cover it in plastic, and store in the refrigerator for up to 2 weeks. TO FREEZE: Leftover slices of cake can be stored in a freezer friendly container and stored in the freezer for up to 6 months. Thaw the cake overnight in the refrigerator.