In a medium saucepan over medium heat, combine coffee and sugar. Stir until sugar has dissolved. Whisk in the cocoa.
1 cup brewed coffee, 1 cup granulated sugar, 1 teaspoon cocoa powder
Remove from heat. Let cool completely.
Stir in dark rum and vanilla extract.
1½ tablespoons dark rum, ½ teaspoon vanilla extract
Transfer to a glass jar and seal tightly with a lid. Store in the refrigerator for up to 1 month.
Mascarpone Cold Foam
In a glass jar or small mixing bowl, combine heavy cream, mascarpone cheese and sugar.
½ cup heavy cream, 1 tablespoon mascarpone cheese, 1-2 tablespoons granulated sugar
Whisk with a milk frother, electric mixer or by hand until stiff peaks form.
Tiramisu Cold Brew
Add ice to a 12-ounce glass. Top with cold brew coffee, leaving about an inch at the top of the glass for the cold foam.
10 ounces cold brew coffee
Stir in tiramisu syrup, to taste. Adjust until it tastes the way you like before moving on.
½ ounce tiramisu syrup
Spoon tiramisu mascarpone cold foam over top.
¼ cup mascarpone cold foam
Dust with cocoa powder and serve.
1 pinch cocoa powder
Notes
Make the syrup ahead. The tiramisu syrup keeps in the refrigerator for up to 1 month. Make a batch and use it all week.Make the cold foam ahead. The mascarpone cold foam can be made up to a day in advance and stored covered in the refrigerator.Syrup to taste. Start with ½ ounce and add more if you want a stronger tiramisu flavor — everyone's sweetness preference is different.