Combine all ingredients except cream in blender, blend over high speed to lightly thicken and melt sugar, then pass through chinois, discard all rosemary.

Transfer to mixing bowl over double boiler, whisk to 85°C or until thickened and airy, then ice bath to cool, stir in cream, taste and adjust as needed.

Transfer to siphon, charge twice, then disperse in flat boxes for service.