Begin by preheating your oven to 350 degrees Fahrenheit. Lightly grease (with butter) AND line with parchment paper the bottoms of TWO 8-inch cake pans (for thicker layers) or THREE 6-inch cake pans.
In a bowl, whisk together the milk and lemon juice and set aside for 5-10 minutes until everything "activates" to create the dairy-free "buttermilk".
In a large bowl, whisk together both the flours, baking powder, apple pie spice, and salt until combined.
In a bowl, add the butter and sugar, beating them together using a hand-mixer (on high-speed), until pale and fluffy, about 2-3 minutes.
Add the eggs (one at a time) followed by the vanilla and oil, mixing until combined. On low-speed, add in the dry ingredients followed by the apple cider and then the 'buttermilk' and continue to mix until combined and the batter is smooth, about 3-4 minutes. NOTE: The batter should be thick, yet slowly run off the whisk once lifted.
Divide the batter evenly into each of the cake pans and bake for 30-35 minutes, or until a toothpick or butter knife comes out clean when tested in the centers.
Remove cakes from the oven and let them rest in the pan for 10 minutes or so before removing the cakes and placing them onto a cooling rack to fully cool. NOTE: Let them cool for at least 1-2 hours in a cool place.
MAKE THE CINNAMON MAPLE BUTTERCREAM:
Simply beat the butter in the bowl of an electric mixer (or using a hand-mixer) on medium-high speed, until smooth and pale. Add in the powdered sugar, cinnamon, maple syrup, and milk, continuing to mix on medium-speed until you reach the desired consistency----smooth and fluffy. NOTE: Add more milk (1 tablespoon at a time if too thick) or powdered sugar (for more thickness).
ASSEMBLY:
Place the first cake layer on your cake stand and evenly cover the top with buttercream. Now, top with 2nd layer and add more buttercream atop that layer, spreading it over the tops and sides of cake, evenly and thinly. NOTE: If making a 3-layer, be sure to repeat step 1 of assembly once again before getting to the final layer.
Once fully frosted, add small little designs of the buttercream using a piping bag + tip around the sides and top of cake. Chill for 5 minutes to ensure that buttercream sets. Top with sliced sliced apples, if desired. NOTE: For a fancy moment or occasion, add florals or greenery atop cake for a Fall vibe!
When ready to serve, remove from the refrigerator. Slice and enjoy!
Bon Appetit!
Notes
STORAGE: Keep cake leftovers stored for up to 4-5 days in the fridge. Keep it in an airtight container to keep the cake from drying out. You can also freeze the cake tightly wrapped in plastic wrap for up to 3 months. Before serving, defrost the cake on the counter.
FLOUR: You can also use cake flour in place of all-purpose flour for a fluffier texture.
APPLE CIDER CUPCAKES: This recipe yields about 30 cupcakes. Simply bake for 18-20 minutes instead, until centers come out clean.
BUTTERMILK: For a dairy-free 'buttermilk', use ½ cup Almond milk + 1 teaspoon lemon juice. For a dairy option-----Add 1 cup of organic heavy cream + 1 tablespoon lemon juice and let sit for 10 minutes, until it thickens.
VEGAN OPTION: To make this cake entirely dairy-free + vegan, simply omit the unsalted butter and eggs and use vegan butter instead and add 1 tablespoon apple cider vinegar to plant-based milk instead of lemon juice. Also, feel free to use coconut oil as a substitute for canola oil, if desired.