Preheat the oven to 350°F (180°C). Spray a 9x13 sheet pan with non-stick spray and set it aside.
Sift the flour into a mixing bowl and add baking powder, baking soda, salt, and mix together.
2 ¾ cup Whole wheat flour, 1 teaspoon baking soda, 1 teaspoon baking powder, ½ teaspoon salt
Prepare the vegan buttermilk Take 1 ½ cup of almond milk in a bowl and squeeze 2 tablespoon of lemon juice. Mix gently and allow it to settle for a minute to curdle.
1½ cup vegan buttermilk
Prepare your flax egg by mixing flaxseed meal with Hot Water and allowing it to sit for a minute to thicken.
Place the banana in a bowl and mash it with a fork, then add sugar and mix well. Add the flax eggs, vegan buttermilk, coconut oil, and vanilla extract. And combine well.
3 large overripe bananas, 1¼ cup organic sugar, ¼ cup coconut oil, 2 teaspoon Vanilla extract or essence
Now mix the dry ingredients with the wet ingredients and whisk until you get an even mix. (whisk with a hand whisk to remove any lumps.)
Pour the batter out into the sheet pan and spread out evenly.
Place into the oven and bake for 30-35 minutes or until a toothpick inserted into the center comes out clean. Check it at 30 minutes it might be perfectly done.
Place the whole sheet pan onto a cooling rack and leave to cool completely before frosting.
Prepare your frosting by adding the powdered sugar, vegan butter, and vanilla extract to the bowl of an electric mixer and starting at slow speed, gradually increase speed until perfectly thick and smooth. If it turns out too thin, add more powdered sugar until it reaches the right thickness.
3 cup powdered sugar, ⅓ cup vegan butter, 1 teaspoon vanilla extract
Frost the cooled vegan banana cake, and enjoy!