In a microwave-safe bowl, place the all-purpose flour and heat it in the microwave for about 1 minute to eliminate any possible bacteria. Allow it to cool.
In a large mixing bowl, combine the softened butter, powdered sugar, and brown sugar. Use an electric mixer to beat them together until creamy and smooth, about 2-3 minutes.
Mix in the vanilla extract until well incorporated.
Gradually add the cooled flour into the butter and sugar mixture, mixing on low speed until combined.
Slowly pour in the milk while mixing until the desired consistency is reached. The dip should be thick but spreadable; add an extra splash of milk if necessary to adjust the texture.
Gently fold in the rainbow sprinkles and mini chocolate chips (if using) until evenly distributed.
Transfer the funfetti dip to a serving bowl and refrigerate for at least 30 minutes before serving for optimal flavor and texture.
Notes
Serve with an assortment of dippable treats such as graham crackers, fruit slices, or pretzels for a colorful and fun dessert spread.