Preparation

• Place hibiscus flowers and 1 cup water in a small saucepan; bring to a boil over high. Remove from heat; cover and let steep 30 minutes. Pour through a fine wire-mesh strainer into a bowl; discard hibiscus flowers. Add 1 cup sugar to infused mixture, and stir until dissolved. Set aside until ready to use.
• While hibiscus mixture steeps, stir together raspberries and remaining ½ cup sugar in a medium saucepan, and let macerate, stirring occasionally, 10 minutes. Cook over medium-low, stirring often, until sugar has dissolved, 3 to 4 minutes. Remove from heat, and let mixture cool to room temperature, about 20 minutes. Transfer mixture to a blender; process until smooth, about 1 minute. Pour through a fine wire-mesh strainer into a resealable container; discard solids. Add hibiscus liquid and corn syrup to raspberry puree; stir until well combined. Cover and refrigerate mixture until chilled, at least 1 hour or up to 12 hours.
• Pour chilled sorbet mixture into frozen freezer bowl of an ice cream maker, and proceed according to manufacturer's instructions. Serve immediately for a soft-serve consistency, or transfer to a shallow container, cover, and freeze until firm, about 2 hours. Sorbet may be stored in an airtight container in freezer up to 3 weeks.