Stick your martini glass into the freezer to chill it.
Fill the cocktail shaker full with ice.
Using the jigger, measure out 3 oz of Peanut Butter whiskey. Pour that into the shaker.
Using the jigger, measure out 1.5 oz of chocolate liqueur. Pour that into the shaker.
Using the jigger, measure out 1 oz of heavy cream. Pour that into the shaker.
Stick the shaker lid on top of the shaker.
Shake it up until the outside of the shaker is cold and icy to touch.
Remove the martini glass from the freezer.
Take the chocolate syrup and drizzle it around the inside of the martini glass.
Remove the shaker lid and put the hawthorne strainer over top of the shaker.
Pour the drink from the shaker into the glass.
Add a peanut butter cup to the rim if desired.