Begin with a (preferably level) frosted cake. The icing should be as smooth as possible. Place the cake, uncovered, in the refrigerator so the frosting can harden a bit.
Test before decorating! Drop a small bead of ganache on a plate and then turn vertically to allow the bead to drip. If the chocolate runs too fast, it’s still too warm, cool longer!
Hold squeeze bottle vertically and drop a single bead of ganache on the very edge of the top of the cake. Squeeze until the bead drizzles over the edge and begins to drip down the side.
Draw a line along the top of the cake to the next point where you’d like your next drip to be (typically only a few centimeters!). Squeeze another bead of ganache over the edge.
Once you have dripped ganache all the way around the cake, drizzle a thin layer of ganache over the surface of the cake. Use an offset spatula to spread it evenly.