Preheat the oven to 350 degrees and line cookie sheets with parchment paper or a silicone mat.
In a medium bowl whisk together flour, baking soda, and salt. Set aside.
In a large bowl, add the melted butter, sugar, and powdered sugar. Using an electric mixer, beat on high for 30-45 seconds.
Add the eggs, egg yolk, and vanilla extract to the butter/sugar mixture. Beat on medium speed for about 45 seconds until well combined.
Add half of the dry ingredients and beat on low until mostly combined. Add the second half of the flour mixture and continue beating until the flour has been incorporated.
With a spatula, gently fold in the fruity pebbles until evenly dispersed throughout the dough.
Cover the bowl and place it in the refrigerator for 30-40 minutes.*
Remove from the refrigerator and scoop out cookie dough balls of about 2 heaping tablespoons or approximately 25 grams. If you will not be frosting, dip the cookie dough ball into the extra bowl of Fruity Pebbles. Place on the baking sheet giving about 2-3” between cookies to allow for spreading.
Bake for 10-12 minutes until edges turn a slightly golden brown. Let them sit on the cookie sheet for about 5 minutes and transfer to a wire cooling rack.