Add the vanilla frosting to a piping bag equipped with the 1A frosting tip, and frost in a swirl pattern around the cupcake.
Add the black icing to a piping bag equipped with the small round tip and pipe a line in the same fashion you did the frosting, going up and around the cupcake to make the “string” for the “lights”.
Place 7-8 M&Ms along the string to make the lights.
Notes
Cool Completely: Ensure your cupcakes are completely cool before frosting. Warm cupcakes will melt the frosting and ruin the design.
Icing Consistency is Key: For the black "string," use a thicker icing or decorating gel. A thin or runny icing will not hold the M&M's well. If your black icing is too thin, try adding a tiny bit of powdered sugar to stiffen it up.
Don't Overfill the Liners: Fill cupcake liners about 2/3 full (or just below 3/4 full). This ensures nicely domed tops perfect for swirling frosting, but prevents them from spilling over.
Quick Swirl: When piping the black string, work quickly and in one continuous line for a smooth, natural-looking string of lights.
Set the Lights: Gently press the M&M's into the black icing. This helps secure them and prevents them from rolling off before the icing has a chance to set.