Cover a 9x9 inch baking pan with parchment paper and spray with cooking spray.
In a large Dutch oven or pot, melt the 8 tablespoons of butter over medium-low heat.
When the butter is fully melted, stir in the marshmallows and stir continuously until the marshmallows are melted and the butter has incorporated. The marshmallows can easily burn, so do not leave them unattended. Turn the heat off and stir in the vanilla extract until combined.
Pour the Cocoa Pebbles into the marshmallow mixture and make sure to gently stir together until the marshmallows fully coat all the Cocoa Pebbles evenly.
Pour the mixture in the prepared baking pan and evenly pat down the cereal so it’s an even level. Cool the pan on the counter for 1-2 hours or refrigerate for 20-25 minutes, allowing the treats to set.
When the treats have cooled, remove the pan. Melt the candy melts according to the package instructions.
Drizzle the melted candy over the Cocoa Pebbles treats in the pattern of your choosing. You can use a toothpick to create a web design or just an abstract design. Immediately cover with sprinkles while the candy is still melted. Allow the candy to harden and cut into 9 even pieces.