Preheat the oven. Set your oven to 375°F (190°C). Lightly butter a small baking dish or use a snug oven-safe skillet.
Prep the apples. Wash and core the apples using an apple corer or a small paring knife. Leave the bottoms intact so the filling doesn’t fall through.
If the apples wobble, slice a thin sliver off the bottom to help them stand upright.
Make the walnut filling. In a small bowl, mix chopped walnuts, brown sugar, cinnamon, a pinch of nutmeg, and a pinch of salt. Stir in vanilla extract if using. Taste and adjust sweetness.
Stuff the apples. Spoon the walnut mixture into each apple cavity and gently pack it in.
Dot the tops with small pieces of butter. If you like extra shine and sweetness, drizzle a little honey or maple syrup over the stuffing.
Add liquid to the dish. Pour water or apple cider into the baking dish around the apples. This helps steam them and creates a light sauce at the bottom.
Bake. Cover the dish loosely with foil and bake for 20 minutes.
Remove the foil and continue baking for another 15–25 minutes, until the apples are tender but not collapsing. Total time will vary depending on apple variety and size.
Check doneness. Pierce an apple with a knife or skewer. It should slide in easily with slight resistance near the skin.
If it’s still firm, keep baking in 5-minute increments.
Finish with brightness. After baking, spoon some of the pan juices over the apples. Add a tiny splash of lemon juice to the pan juices if you want a brighter flavor contrast.
Serve. Enjoy warm. Top with ice cream, whipped cream, Greek yogurt, or a drizzle of cream.
A little extra cinnamon on top never hurts.