Hold an empty, dry rocks glass on its side. Using a spoon or the bottle if it has a pour spout, drizzle chocolate syrup around the inside wall of the glass with one hand while you rotate the glass with your other hand. drizzle chocolate syrup around the inside wall of the glass, while rotating it.

Pour peanut butter whiskey into the prepared glass. (Be careful not to pour it on your chocolate drizzle — aim for the middle.)

Carefully lower in a large ice cube. Top with bitters.

Garnish with a sprinkle of chocolate shavings and a peanut butter cup.