Preheat oven to 350°F. Line an 8×8 baking pan with parchment.
Cream butter and sweetener until light and fluffy.
Add the egg and vanilla; mix until smooth.
Add almond flour, coconut flour, baking powder, and salt; mix into a soft dough.
Press dough evenly into the prepared pan.
Bake 18–22 minutes, or until edges are lightly golden.
Cool completely before frosting.
For frosting: beat cream cheese, butter, sweetener, and vanilla until smooth.
Spread frosting over cooled bars and top with sugar-free sprinkles.
Slice into squares and serve.