Preheat your oven to 350°F (175°C) and prepare baking sheets with parchment paper.

Combine softened unsalted butter, granulated sugar, and brown sugar in a large mixing bowl and beat until light and fluffy.

Add one egg and vanilla extract, mixing until fully incorporated while scraping down sides of the bowl.

Slowly add all-purpose flour to the mixture, mixing until just combined to form a thick dough.

Fold in the crushed Fruity Pebbles cereal until evenly distributed.

Scoop mounds of dough onto prepared baking sheets, spacing them about 2 inches apart. Bake for 10 to 12 minutes.

Cool cookies on sheets for about 5 minutes, then transfer to a wire rack to cool completely before frosting.