Preheat oven to 350 degrees Fahrenheit. Line cupcake tin with liners and set aside.
Make vegan buttermilk: In a large measuring cup add apple cider vinegar to almond milk and stir. Let sit for about 10 minutes and the mixture with "curdle" similar to buttermilk.
Meanwhile, in a large mixing bowl, whisk together the cake flour, baking powder, baking soda, and salt.
In a separate mixing bowl, combine the vegan buttermilk, grapeseed oil, vanilla, and sugar. Whisk until combined.
Slowly pour the wet ingredients to the dry ingredients. Whisk until just incorporate (do not overmix!) The batter with be thick and pourable with some clumps.
Using an ice cream scoop, fill each liner with batter about 3/4 way. Bake for 18-20 minutes. To check for doneness, insert a toothpick into the center of a cupcake. If it comes out clean the cupcakes are ready!
Remove from the oven and let cool 5-10 minutes before transferring to a cooling rack.
To Make the Frosting:
Using a stand or hand mixer, beat the butter until fluffy.
Add powdered super 1 cup at a time. It will look kinda crumbly at first but this is okay!
Once you add in the rest of the sugar, the mixture will be super thick and fluffy. Add in 2 Tablespoons of almond milk and vanilla. If you need more liquid, add the last Tablespoon of almond milk.
You’ll know it’s ready when it has a light fluffy texture that stands up nicely on the end of the whisk. You don’t want it too soft or you can’t pipe with it onto your cupcakes!
Insert your frosting tip into the frosting bag and snip off the tip. Fill a frosting bag about 1/3 of the way frost cupcakes once they are completely cooled.
Serve immediately. Leftovers keep in the fridge for about 3 days. Cupcakes can be stored in the freezer for about 2 months without frosting.
To substitute cake flour:Replace that 2 Tbsp. with corn starch. If you use this method you must sift it at least twice. This will mix it together properly and take out any granules that can be in all-purpose flour.For 9 inch Cake- fill about 3/4 of the way (note this is for a regular 9-inch cake pan that is about 2.5 inches tall): Bake 28-30 minutes or until a toothpick in the center comes out clean. For 9x13 inch sheet cake- Bake 32-35 minutes. Please note that glass or metal pans will vary cook time. You should watch the cake by setting your timer to lower end of these cooking instructions and give it 2-3 minute increments more until your toothpick comes out clean.