Before starting, make sure all of your ingredients for this vegan orange cake are at room temperature.
Preheat the oven to 350 degrees Fahrenheit. Grease and flour two 9-inch cake pans.
In a small bowl, whisk or whip together the aquafaba and cream of tartar vigorously until the aquafaba is fluffy and foamy (soft peaks are ideal), and set aside.
In another small bowl, stir together the soy milk, orange juice, 2 tsp vinegar, orange extract, and butter flavor, and set aside. The soy milk will curdle a little bit; this is normal.
Sift all of the dry ingredients (including the sugar) into a mixing bowl and stir well, sifting a second time if the mixture still appears lumpy. Don't skip this step - sifting is important!
Add the vegetable oil and shortening into the bowl. Using a mixer or a strong utensil, mix everything together well until it starts to resemble wet sand. Make sure to scrape around the bottom of your mixing bowl to get rid of flour pockets hiding out there. Continue until fully smooth.
Add 1/3 of the wet ingredients to the bowl and mix until combined. Add another 2/3 and repeat. Finally, add the remaining 1/3 and mix until the batter is very smooth and runny, which will take a minute or two.
Whisk the foamy aquafaba mixture into the cake batter until mixed in evenly (if you only fold it in, you might get streaks or a gummy layer - mix well if needed). Divide the cake batter between your two cake pans.
Bake the orange cake layers for approximately 24-28 minutes, or until a toothpick inserted into the center comes out clean and dry. Be sure not to open the oven door at all until at least 20 minutes have passed.
Let the cakes cool in their pans on top of a cooling rack for about 10 minutes. You can then run a sharp knife around the edges of the pans before very gently inverting the cakes to cool completely. I recommend lightly flouring or spraying your cooling rack before flipping the cakes onto it; they are very moist and have a tendency to stick. After flipping them over, gently peel off the parchment paper.
These cakes can be layered and frosted once completely cooled (and the layers can be gently evened out if needed, although they tend to bake pretty flat). Take care in handling them; they are rather delicate. Leftover cake can be stored covered in the fridge for a couple of days. If your layer cake is fully frosted it can also be stored covered at room temperature. If stored in the fridge, it's recommended to bring it to room temperature before slicing, to reduce crumbliness.
Notes
ORANGE COLOR: Add orange food coloring if desired to give the cake an orange hue. Please follow the instructions on your particular food coloring for how much, when and how to add it; brands may vary.AQUAFABA - This is the cooking liquid from beans; it has properties similar to egg whites. For this recipe, I recommend draining the liquid from a can of low-sodium or unsalted white beans (cannellini, navy, etc.) - it will have the lightest color.NUTRITION - Nutrition facts do not include any sort of frosting or icing.