The instagram for the cocktail says "Vermouth infused with Pop Corn (Sous-Vide at room temperature for 24 hours)".
I've not had this drink, so am just guessing at a starting point... Put a handful of popcorn and 50 g of clarified butter per 250 mL of vermouth, vacuum-sealed (using either a chamber sealer and bag or the jar sealing attachment of a cheaper vacuum unit), left for a day, & double-strained. Possibly add salt.
I'm impatient, so would probably try rapid infusion via iSi instead & tweak ratios to personal taste (or taste memory for those who have had the drink).