Make the glaze while the mascarpone filling is chilling, because it needs to cool a bit after making. Combine the sugar, juices, cornstarch and salt in a saucepan over medium-low heat. Whisk until the cornstarch dissolves and bring the mixture to a boil. Let it boil for 1 to 2 minutes, until it starts to thicken. (It will thicken more as it sits and cools). Remove from the heat and stir in the vanilla bean paste. Let cool for 10 minutes, but not much longer.