Whisk the all-purpose flour, baking powder, baking soda, and salt together in a small or medium bowl.
2 cups unbleached all-purpose flour, 2 teaspoons baking powder, 1 teaspoon baking soda, ½ teaspoon kosher salt
Whisk the plant-based buttermilk, organic cane sugar, vanilla extract, remaining lemon juice, and coconut oil together in a large bowl.
1 cup plant-based milk, ⅔ cup organic cane sugar, ¼ cup coconut oil, 3 tablespoons + 1 teaspoon fresh lemon juice, 1 teaspoon pure vanilla extract
Slowly add the dry ingredients to the wet in batches, stirring to incorporate each time. A few small lumps are acceptable, but the batter should be mostly consistent.
Stir in the lemon zest.
3 ½ tablespoons lemon zest
Fold in the whipped aquafaba until incorporated.
7 tablespoons aquafaba
Gently fold in 1 cup of the blackberries (including the halved berries) until incorporated throughout the batter.
1 ¼ cup fresh blackberries
Spoon the batter into the loaf pan. Bake for 45-55 minutes on the center rack in the oven. Test with a toothpick or skewer. The bread should be lightly browned on the top and edges, and the toothpick should be clean upon removal.
Allow to cool for up to 10 minutes in the loaf pan before transferring to a wire rack.