Prevent blackberry lemon bread from sinking in the middle by following a few simple steps. (1) First, don’t overmix the batter. The mixing should be done by hand (not in a stand or hand mixer), and each step should be stirred just until combined. (2) Bake the bread in the center of the oven and check for doneness by inserting a toothpick into the middle of the loaf before deciding if the bread is done. The toothpick or skewer should be clean when removed from the loaf. (3) If your bread sinks after following these steps, check the date on your leavening agents (baking powder and baking soda) and (4) make sure you whipped the aquafaba to the stiff peak stage.