Mix butter, sugar, yogurt, and vanilla in a large bowl with electric mixer.
Add in dry ingredients, and mix until evenly blended. *Batter will be thick.
Line a square 8x8 inch pan with parchment and spray a little nonstick, then spread batter out in pan.
Bake at 350 degrees for around 20 minutes, or until firm and slightly golden.
Cool completely before frosting.
To make frosting, blend all ingredients together with an electric mixer until smooth.
Spread generously over top of your cookie bars, add sprinkles, and cut into squares.