Line an 8×8-inch baking dish with parchment paper.
Combine dark chocolate, condensed milk, and butter over low heat.
Stir in vanilla extract.
Spread mixture evenly into pan.
Melt white chocolate, divide, tint red and gray.
Drizzle and marble with a skewer.
Sprinkle edible shimmer.
Refrigerate 2 hours until firm.
Cut into neat squares and enjoy.
