Preheat your oven to 350°F (175°C). Lightly spray a 9x13-inch baking dish with cooking spray.
In a medium bowl, mix the light yellow cake mix, unsweetened applesauce, and one egg until combined.
Spread the mixture evenly into the prepared baking dish. The dough will be thick and sticky, so you might need to use a spatula or your hands (lightly sprayed with cooking spray) to press it down.
In a large bowl, beat the reduced-fat cream cheese until smooth. Add the eggs and vanilla extract, and continue to beat until well combined. Gradually add the powdered sugar substitute) and mix until fully incorporated. Pour in the melted light butter and beat until the mixture is smooth and creamy.
Pour the filling over the crust and spread it out evenly. Bake in the preheated oven for 35-40 minutes, or until the top is golden brown and the center is set (it will still be a bit gooey). Remove from the oven and let it cool completely in the baking dish.
Once cooled, cut into squares and dust with additional powdered sugar if desired. Enjoy!
This makes 12 Bars. On WW, each bar is 6 WW Points. Enjoy!