Line an 8 × 8-inch baking dish with parchment paper, leaving some overhang on the sides, and lightly grease the parchment.

Add the white chocolate chips, mini marshmallows, and butter to a large microwave-safe bowl.

Microwave for 1 minute, then remove the bowl and stir with a lightly greased spatula.

Return the bowl to the microwave and heat in 30-second intervals, stirring well after each interval, until the mixture is melted and smooth.

Let the melted mixture rest for about 1 minute.

Fold in the chopped gumdrops just until evenly distributed.

Transfer the mixture to the prepared baking dish.

Use a lightly greased spatula to press the candy into a flat, even layer.

Cover and refrigerate for at least 2 hours, or until firm enough to slice cleanly.

Lift the candy from the pan using the parchment overhang and peel away the parchment.

Cut into small bite-sized squares with a sharp knife, lightly greasing or wiping the knife between cuts if needed.