Bosc pears are firmer than other pear varieties, making them ideal for poaching in liquid. Look for firm-yet-ripe pears that yield slightly when you press the end opposite the stem. Perfectly ripe pears need little more than a slow simmer in wine with spices. Despite their simplicity, these pears look incredibly gourmet served in a shallow bowl surrounded by the burgundy sauce.
Prepare the pears. Peel the pears and halve them lengthwise. Remove the seeds and core. Set the pear halves in the Dutch oven and pour the red wine on top. Add the vanilla, sugar, and star anise (if using).
Poach. Bring the wine to a low simmer over medium heat. Cover the pot, leaving the lid slightly ajar. Cook for 8 minutes, checking frequently to ensure the liquid is bubbling only slightly. Flip the pears and cook for about 8 minutes more, until a skewer pierces the pear flesh very easily. Transfer the pears to shallow serving bowls.
Reduce the wine. With the lid off, bring the liquid to boil. Cook for about 15 minutes, just until the sauce thickens enough to coat the back of a spoon. Drizzle a large spoonful of sauce over each pear and serve. Refrigerate leftovers with the sauce for up to 3 days.