How to make 19-calorie chocolate brownies for weight loss

½ cup unsweetened cocoa powder, ½ cup unsweetened applesauce, ¼ cup oat flour, 2–3 tbsp zero-calorie sweetener, to taste, 1 egg white, ½ tsp vanilla extract, ½ tsp baking powder, A pinch of salt, 2–3 tbsp water or unsweetened almond milk
Optional: A few sugar-free chocolate chips