1. Peel the pears, leaving the stems intact.
2. Place the pear nectar in the bottom of a microwave or conventional stove-top steamer, and transfer the pears to the steamer. Cover and cook at high power or over medium-high heat for 4 to 5 minutes, or until tender.
3. Drain the pears, reserving the nectar. Cover the pears and chill for several hours or overnight.
4. To make the sauce, place the cornstarch and sugar in a small saucepan, and stir to mix well. Stir in 1/3 cup of the reserved nectar, and cook and stir over medium-low heat until the mixture is thick and bubbly. Stir in the raspberries, and cook and stir for another minute or 2, or until thick and bubbly.
5. Place the chilled pears in individual serving dishes, and pour the warm sauce over the fruit.