Line an 8×8-inch pan with parchment paper, leaving overhang.
Combine dark chocolate, condensed milk, and butter in a saucepan over low heat. Stir until smooth.
Add vanilla extract and optional black gel for depth.
Spread the mixture evenly into the pan.
Melt white chocolate in short bursts, drizzle on top, and swirl gently with a skewer.
Dust with silver edible glitter while warm.
Refrigerate 2 hours or until firm. Lift and cut into squares.
