Grease & parchment line your cake pans *see notes for success for pan sizes
Preheat the oven to 350°F
Prepare your favorite buttercream recipe as per the instructions & add the zest along with the juice at the last stage of mixing. Whip to smooth
Prepare the cake batter~ Note: All of your ingredients should be at room temperature before mixing Cream the vegan butter with the coconut oil & sugar on high speed until light and fluffy approx 5 minutes Combine the plant milk with the lemon juice, extract & zest & then in a separate bowl combine the cornstarch with the aquafaba.
Add the cornstarch/aquafaba mixture to the creamed butter mixture on low speed & once it is incorporated whip on high speed to emulsify. *the mixture will look severely curdled but will come together to a smooth silky batter by whipping on high speed. Be patient!
Meanwhile sift together both flours, the baking powder & salt and then add about 1/3 of the dry ingredients to the mixer bowl while mixing on low-medium speed.
Now add half of the milk/lemon mixture & mix just until incorporated
Add another 1/3 of the dry ingredients mixing just until incorporated lightly then add the last of the liquid & then the last of the dry
Whip on high for 10 seconds to develop the batter
Pour the batter into your prepared pans & bake in the preheated 350° oven for 25-35 minutes or when a toothpick inserted into the center comes out clean. *for larger sized pans I like to turn the oven temperature down to 325℉ midway through baking to ensure it does not over brown on the top & edges
Cool in the pan then flip out onto your serving platter then iice with buttercream, or build a layer cake as you desire!