Preheat oven to 400°. Core apples and peel off and discard the top third of their skin. Place in a baking dish.
Cut butter into small pieces, placing a little inside each apple and the rest on top, dividing it evenly among them.
Zest orange, setting zest aside, then squeeze juice from it and pour over apples. Add zest to baking dish, either in one long ribbon or in smaller pieces.
Drizzle honey on top of and into the cavity of each apple. Pour calvados into baking dish, over and around apples. Scatter cloves, star anise, and cinnamon around the apples, distributing them evenly.
Coarsely chop pistachios. Sprinkle over apples, making sure that some fragments fall into the hollowed-out cavities of each one.
Bake in oven for 45–60 minutes, basting every 15 minutes or so to keep apples from drying out, or until apples are tender when pierced with a knife.
Remove from oven. Liquid in the baking dish should have reduced by this time to a slightly thickened, syrupy sauce. Place each apple on a dessert plate and spoon the sauce over and around apples. Serve warm or at room temperature.