Preheat your oven to 350°F (175°C) and lightly grease or line an 8x8-inch baking dish.
In a large mixing bowl, whisk together the flour, sweetener, baking powder, baking soda, and salt.
Add in the applesauce, oil, and vanilla extract. Stir until a thick batter forms.
Fold in the rainbow sprinkles gently, reserving a few for topping.
Spread the batter evenly in the prepared baking dish and sprinkle remaining sprinkles on top.
Bake for 22–25 minutes or until a toothpick inserted into the center comes out clean.
Let the blondies cool completely in the pan before slicing and serving.