Add cream and rosemary sprigs to a small saucepan. Heat on medium until cream just begins to simmer; remove from heat. Transfer mixture to a glass bowl and allow to cool for about 30 minutes. Strain the mixture and return cream to the small bowl; cover and refrigerate until cold, at least 2 hours.
Place cream in a 1 pint whipped cream dispenser. Charge with 1 N2O cream charger, shake and serve.