Combine the wine, sugar, star anise, vanilla, salt, and 3/4 cup water in a 3- to 4-quart saucepan that’s wide enough to fit the halved pears in a snug single layer. Bring to a simmer over medium-high heat, stirring occasionally to dissolve the sugar. Reduce the heat to low, add the pears, and cook at a bare simmer (basting occasionally if there are any unsubmerged parts) until just tender when pierced with a wooden skewer or toothpick, 15 to 30 minutes depending on ripeness. Remove the pot from the heat and allow the pears to macerate in the poaching liquid for at least 2 hours, or discard the star anise and refrigerate in the liquid overnight.
Transfer 2/3 cup of the poaching liquid to a small saucepan and boil over high heat until reduced by half and slightly syrupy, about 5 minutes. Let cool. Spoon a little syrup onto each of four serving plates. Place the pears, cut side down, on a cutting board and, holding the knife at a 45-degree angle, slice them lengthwise about 1/3 inch thick almost to the stem, so the slices remain attached at the stem end. Transfer the pears to the serving plates and press down gently to fan them out, exposing the lighter centers. Sprinkle the pears with the pistachios and serve with a scoop of ice cream.