Step 1: Line an 8x8 inch baking pan with parchment paper, allowing an overhang on the sides for easy removal. Lightly grease the parchment paper if desired.
Step 2: In a large microwave-safe bowl, combine the sweetened condensed milk, chocolate chips, and butter. Microwave in 30-second intervals, stirring thoroughly after each, until the mixture is completely smooth and melted. Alternatively, melt the ingredients together in a saucepan over low heat or in a double boiler.
Step 3: Remove from heat (or microwave) and stir in the vanilla extract until it's fully incorporated into the chocolate mixture.
Step 4: Divide the melted fudge mixture evenly into three separate small bowls. Add a few drops of blue food gel to one bowl, purple to another, and black to the third. Mix each color until vibrant and evenly distributed.
Step 5: Dollop spoonfuls of each colored fudge mixture randomly and alternately into the prepared baking pan.
Step 6: Using a knife or a skewer, gently swirl the colors together to create a mesmerizing galaxy effect. Be careful not to overmix, as this can blend the colors too much.
Step 7: Generously sprinkle the top of the fudge with edible glitter or silver/white sprinkles to create the illusion of stars in your midnight galaxy.
Step 8: Refrigerate the fudge for at least 2 hours, or until it is completely firm. Once set, use the parchment paper overhang to lift the fudge from the pan and cut it into small squares for serving.