Preheat the oven to 350 degrees. Line an 8x8-inch baking pan with parchment paper, leaving a slight overhang for easy removal. Lightly grease the parchment.

Melt the butter in a microwave-safe bowl or saucepan until just melted. Let it cool slightly.

In a large mixing bowl, whisk together the melted butter, granulated sugar, brown sugar and vanilla extract until smooth and combined.

Add the eggs one at a time, mixing well after each addition.

Fold in the flour and salt until just combined. Avoid overmixing to keep the blondies soft.

Gently fold in the Fruity Pebbles cereal, white chocolate chips, and mini marshmallows until evenly distributed throughout the batter.

Spread the batter evenly into the prepared baking pan. Use a spatula to smooth the top.

Bake for 25–30 minutes, or until the edges are golden and a toothpick inserted near the center comes out with just a few moist crumbs.

Allow the blondies to cool completely in the pan. Once cool, lift them out using the parchment paper.

Drizzle the melted white chocolate over the top. Let it set before slicing into squares.