Before you start getting excited about sprinkles and frosting, cake liner has nothing to do with dessert and everything to do with your eye makeup. It's great for those who want to achieve a perfectly lined eye without having the steady hand required by many liquid eyeliners.
According to The Beauty Department, cake liner is merely a matte shadow that's applied with a wet pointed liner brush. It makes for an easy application that even beginners shouldn't have trouble with.
To get the look, pick up a shadow like POP Beauty – Eye Cake. You'll be able to play with the different shades to get the exact effect you want. You'll also need a liner brush, like Paula Dorf – Eye Liner Brush.
Wet the brush under running water, then swirl it around in the shadow of your choice. The news source suggests practicing a few sweeps across the back of your hand before you start on your eyes, just to get a handle of how it will be applied. Finally, sweep the brush from the inner corner of your eye to the outer corner, extending it out if you want.