Using an ice cream scoop, put 1/2 cup of sherbet into each glass. Scoop 1/2 cup of vanilla ice cream on top of the sherbet. Pour 1/3 cup club soda on top of the ice cream. Drizzle each glass with 2 tablespoons of raspberry syrup and garnish with fresh raspberries. Serve immediately with straws and sundae spoons.
In a small saucepan, whisk together the orange juice and cornstarch until smooth. Add the raspberries, raspberry jam and sugar. Bring the mixture to a boil over medium-low heat, stirring frequently. Reduce the heat to medium-low and simmer for 5 minutes. Pour the mixture through a fine-mesh sieve into a small bowl, pressing on the solids with a wooded spoon to extract as much liquid as possible. Cool the syrup for 30 minutes.