These birthday cake blondies taste like a classic buttery blondie filled with sprinkles and topped with classic vanilla buttercream and even more sprinkles!
In a small bowl, whisk the flour, baking powder and salt together.
In a medium or large mixing bowl, whisk the melted butter and sugar together until fully combined. Whisk in the egg and vanilla until smooth.
Add the dry mixture to the wet. Fold in the sprinkles. Pour into a 9x5 loaf pan.
Bake at 350 F/ 177 C for 28-35 minutes.
Cool in the pan for 20-25 minutes. Lift out of the pan to cool completely.
Make the vanilla buttercream by creaming butter, powdered sugar, vanilla extract and milk together until smooth and creamy.
Spread the buttercream on top of the cooled blondie bars. Top with more sprinkles.
Cut into bars and enjoy!
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