My sister-in-law pours this 4 ingredient concoction at every backyard barbecue and it has completely replaced the dessert table.

Chill your mason jars, diet cola, coconut syrup, lime, and heavy cream for at least 30 minutes so everything is good and cold. This helps the drink stay fizzy and gives you those pretty creamy ribbons instead of everything melting together right away.
Fill two mason jars about 2/3 full with ice cubes or crushed ice and set them on your kitchen counter. You want enough ice so the dark cola and cream can swirl around it and create that marbled look against the glass.

In a small measuring cup or bowl, stir together the coconut syrup and fresh lime juice until well combined. This makes a bright, sweet base so the lime doesn’t just sit on top of the cola.
Divide the coconut-lime mixture evenly between the two mason jars, pouring it right over the ice.
Slowly pour 1 cup of chilled diet cola into each jar. Tilt the jar slightly and pour down the side to keep as much fizz as possible. You’ll see the dark liquid bubble up around the ice.
Cola being poured into an ice-filled mason jar
Cola being poured into an ice-filled mason jar
Give each jar a gentle stir with a long spoon—just a few turns—to mix the coconut-lime with the diet cola while still keeping some lighter and darker streaks.
Right before serving, slowly pour about 2 tablespoons of very cold heavy cream into the center of each jar. Let it sink and swirl on its own for a moment; you’ll see creamy ribbons curling through the fizzy cola against the sides of the mason jars.

If you like, give the drink one or two gentle stirs to slightly blend the cream without losing the marbled look. Serve immediately, while the glass is beaded with condensation and the top is still foamy and swirled.
Variations & Tips