Add a half an ounce of sambuca to create your next layer. There are a number of ways to get this layered effect. You can just slowly pour the ingredient down the side of the glass, but this risks disrupting the grenadine. If you pour the alcohol slowly down the handle of a spoon it helps it disperse without ruining your base. Or, turn the spoon upside down over the shot glass, and slowly pour the half an ounce over the convex side, letting it drizzle in.