Line an 8x8-inch square baking dish with parchment paper, ensuring the sides are covered, and lightly grease the surface; set aside.

Combine butter, mini marshmallows, and white chocolate chips in a large microwave-safe mixing bowl. Heat in the microwave for 1 minute, then stir thoroughly using a greased spatula.

Continue microwaving in 30-second bursts, stirring each time, until the mixture becomes fully melted and silky in texture.

Allow the melted mixture to rest and cool slightly for approximately 1 minute before folding in the chopped colorful candies.

Transfer the mixture into the prepared baking dish and gently press it into an even layer with the spatula.

Cover the dish with plastic wrap and refrigerate for at least 4 hours or overnight for best results.

Once firm, lift the candy slab out using the edges of the parchment paper. Discard the paper and cut the candy into small, bite-sized pieces. Store in an airtight container to maintain freshness.