Begin by lining a 9x13 pan with parchment paper. Lightly spray it with nonstick cooking spray and set it aside.

In a large pot, melt your butter. Once melted, stir in two teaspoons of vanilla extract. Keep stirring for an additional thirty seconds until the sizzling subsides.

Add in one bag or half of your marshmallows, mixing until almost completely melted before adding the rest. Stir until all the marshmallows are entirely melted. If needed, return to low heat.

Now, add the Fruity Pebbles 2 cups at a time, stirring lightly until combined. Repeat until everything is evenly mixed.

Pour the mixture into the 9x13 pan. With lightly wet hands, gently press it into the pan's edges, being careful not to crush it.

Place the white chocolate in a heatproof bowl. Microwave for 30 seconds, stir, and repeat until completely melted. Set it aside for 3 minutes to cool to room temperature.

Using a spoon, drizzle the melted white chocolate over the treats. Sprinkle on rainbow sprinkles and extra Fruity Pebbles. Now, it's time to enjoy these delicious treats!