TO PREPARE THE PEARS: Cut a slice from the bottom of each pear so that it will stand upright in the poaching pan. Peel the pears from the base toward the stem, leaving the stem intact. In a saucepan just large enough to hold all the pears standing up but no larger, combine the wine with enough water so that the pears will be covered up to the base of the stems. Add the sugar and, over low heat, stir just until the sugar has dissolved. Add the vanilla bean and lemon zest. Place the pears in the wine and bring the liquid to a slow simmer. Simmer, turning occasionally to be sure the pears take on the color of the wine evenly, until they are tender, 15 to 25 minutes, depending on how ripe the pears are. Transfer the poached pears to a plate.

REDUCE THE LIQUID over high heat until it is syrupy. It will thicken further as it cools, so don't reduce it all the way down. Remove the vanilla bean and lemon zest. (Both the pears and the syrup may be refrigerated for up to 24 hours before serving.)

TO MAKE THE POLENTA: In a medium-size heavy saucepan, combine the milk, water, salt, and 1 tbsp of the sugar and bring the mixture to a boil. Reduce the heat and, when the liquid is simmering, sprinkle in the polenta in a very slow, thin stream, whisking constantly in the same direction until all the grains have been incorporated and no lumps remain. Reduce the heat to very low. Switch to a wooden paddle and stir thoroughly every 1 or 2 minutes for 15 to 20 minutes, or until the mixture comes away from the sides of the pan and the grains of polenta have begun to soften. Stir in the butter, allspice, cloves, and ginger and remove from the heat. The mixture will be so thick that the paddle will stand upright for 2 or 3 seconds.

RINSE AN 8 x 4-1/2-INCH LOAF PAN with cold water and shake dry. Mound the polenta into the pan, smoothing the top with a spatula repeatedly dipped into very hot water. Cover with a tea towel and allow to rest for at least 2 hours at room temperature or up to 24 hours in the refrigerator.

RUN A KNIFE around the edge of the loaf pan to loosen the polenta and invert it on a cutting board. Cut the polenta into twelve 3/4-inch slices and let them dry on a rack for 1 hour.

WHEN READY TO SERVE, preheat the broiler to high heat.

GRILL THE SLICES for 7 minutes on 1 side, or until they have just started to turn golden. Turn to the other side and sprinkle each one evenly with 1/4 teaspoon of the remaining sugar. Grill for 6 minutes more, until the sugar is bubbling and caramelized, watching carefully to be sure that the sugar does not burn. Transfer 2 croûtes, browned side up, to each of 6 warmed dessert plates and place a poached pear in between the croûtes. Drizzle about 1 tbsp of the syrup over the stem of each pear and serve immediately.