Preheat oven to 350°F (175°C). Line two large baking sheets with parchment paper.

In a large bowl, whisk together the melted butter, brown sugar, and granulated sugar until smooth. Whisk in the egg and vanilla extract.

In a separate bowl, sift together the flour, cocoa powder, baking soda, and salt.

Gradually fold the dry ingredients into the wet ingredients using a spatula just until combined. Do not overmix. Gently fold in the rainbow candy chips.

Scoop 3-tablespoon mounds of dough onto the prepared baking sheets, spacing them 2-3 inches apart. Bake for 10-12 minutes until edges are set but centers are still soft.

Let cookies cool on the baking sheet for 10 minutes before transferring to a wire rack to cool completely.

For the glaze, microwave chocolate chips and heavy cream in 20-second intervals, stirring in between, until smooth and glossy. Let cool for 5 minutes to thicken slightly.

Spoon warm glaze over the cooled cookies, spreading it slightly. Immediately top with extra rainbow candy chips. Let the glaze set before serving.