01 - Place the softened unsalted butter in a large mixing bowl. Beat with a hand mixer or stand mixer on medium speed until creamy, pale, and light in texture, approximately 2 minutes.
02 - Gradually add the sifted powdered sugar, 1 cup at a time, mixing on low speed after each addition until fully incorporated and no dry pockets remain.
03 - Pour in the whole milk and vanilla extract. Increase the mixer speed to medium-high and beat until the frosting is smooth, fluffy, and spreadable, about 2 to 3 minutes. Scrape down the bowl as needed.
04 - Using a spatula, gently fold 3/4 cup of Fruity Pebbles cereal into the frosting until the pieces are evenly distributed throughout. Avoid overmixing to keep the cereal from breaking down.
05 - Spread or pipe the frosting onto completely cooled cupcakes, cakes, or cookies using an offset spatula or piping bag fitted with your preferred tip.
06 - Scatter the remaining 1/4 cup of Fruity Pebbles over the frosted surface just before serving to preserve the signature crunch and vibrant color.