We roast Anjou, Comice, or Bartlett pears for this simple dessert in any number of Italian passiti, or sweet dessert wines — vin santo from Tuscany, recioto di soave from the Veneto, or any of the nonsparkling moscati. The prices and delicate flavors of these wines vary; choose one that suits your budget and taste.
Preheat the oven to 375 degrees.
Put the sugar, lemon juice, and the dessert wine in a medium baking dish and stir until the sugar dissolves. Split the vanilla bean lengthwise and scrape the seeds into the dish, then add the pod. Use a measuring spoon or a melon baller to scoop out the core. Arrange the pears in the dish in a single layer, cut side down. Spoon the wine over the pears. Scatter the butter in pieces around the pears.
Roast the pears, basting them once or twice, until they are tender and the juices are syrupy, about 1 hour. Let the pears cool before serving them.