Heat the oven to 375°F. Arrange the cored apples upright in a snug baking dish.
In a bowl, mix the brown sugar, ground cinnamon, ground nutmeg, kosher salt, and raisins until evenly combined.
Pack the sugar–raisin mixture into the cavities of the apples, mounding slightly on top.
Divide the unsalted butter into 4 pieces and place one piece on top of each stuffed apple.
Stir the vanilla extract into the apple cider, then pour the liquid into the baking dish around the apples.
Bake until the apples are tender but still hold their shape, 35–45 minutes, basting once or twice with the pan juices; a skewer should slide in with little resistance.
Spoon the pan juices over the apples and serve warm with vanilla ice cream for serving.