Add apple cider into a small saucepan over medium heat. Bring to a simmer with the lid off, and then continue to let the cider simmer until it has reduced to just a half cup (this will take 15-20 minutes, depending on your pan and stove). Once the cider has reduced, remove it from heat and transfer into a large liquid measuring cup or bowl to cool completely.
After the cider has cooled, whisk in the sour cream, applesauce, and vanilla extract until smooth. Set this mixture aside for now.
In a medium bowl, whisk together the flour, baking powder, salt, and spices until they're evenly distributed.
Preheat oven to 350℉(177℃). Grease three 6" round cake pans and line with parchment cake liners.
In the bowl of a mixer, cream the butter and sugars together until light and fluffy, around 3 minutes. Make sure to scrape down the sides of the bowl every minute.
Add the eggs, one at a time, fully beating in each egg before adding the next. The mixture may split a little but it will come back together once you add the oil and maple syrup.
With the mixer running on medium-low speed, start slowly drizzling in the oil, one tablespoon at a time. Then slowly drizzle in the maple syrup as well, making sure not to add all of it at once. Increase the mixer speed once everything has been added and continue beating for 1-2 minutes, until creamy and smooth.
Alternate adding ⅓ of the flour, half of the cider mixture, another ⅓ flour, the remaining liquids, and the remaining flour. Beat together until smooth but do not over mix.
Divide the batter evenly between the cake pans. Use a food scale to help ensure each pan has the same amount of batter. Bake for 30-33 minutes, until the cakes are set. Allow them to cool completely before frosting.