In a large saucepan combine the port, wine, 1 cup of the sugar, star anise, cinnamon, thyme, lemon zest, the vanilla bean and seeds. Bring to a boil, then reduce the heat and simmer for 15 minutes.
Add the pears and simmer until the pears are cooked through, about 25 to 30 minutes. Turn off the heat and let cool in the poaching liquid.
Before serving, remove the pears from their poaching liquid and reduce the liquid to a syrup. Strain into a small bowl.
Combine the mascarpone and remaining sugar in a small bowl. Dollop a small amount of the mascarpone on each plate and arrange a pear half on top to prevent it from sliding around the plate. Garnish the pears with a large dollop of the mascarpone, and drizzle with the reduced poaching liquid. Shave the chocolate over the mascarpone and serve.