Line an 8×8-inch baking dish with parchment paper, leaving some overhang for easy lifting later. In a saucepan over low heat, melt dark chocolate chips, sweetened condensed milk, and butter until smooth. Stir in vanilla and pour into the pan, smoothing the top.

Melt white chocolate chips in another saucepan, then divide into two bowls. Tint one red and the other gray or black. Drizzle both colors over the dark base, then gently swirl with a knife or skewer to create a marbled “lunar eclipse” effect—don’t overmix.

Dust lightly with edible silver glitter or luster dust for a night-sky shimmer. Chill for at least 2 hours, or until firm, then lift from the pan and cut into squares. Serve slightly chilled for the creamiest texture.