01 - Set oven to 350°F to prepare for baking.
02 - Core each apple carefully, keeping the bottom intact to create a hollow well for the filling. Stand the apples upright in a baking dish.
03 - Combine oats, nuts, raisins, brown sugar, cinnamon, nutmeg, and salt in a medium bowl. Pour in melted butter and 1/4 cup maple syrup, stirring until evenly blended and slightly sticky.
04 - Distribute the filling mixture among the cored apples, spooning it in and packing gently to fill each cavity completely.
05 - Pour apple juice or water into the bottom of the baking dish around the apples. This prevents sticking and generates steam during baking.
06 - Cover the baking dish loosely with aluminum foil and bake for 25 minutes to begin softening the apples.
07 - Remove the foil and continue baking for 10-12 minutes longer, until apples are tender when pierced and the filling tops are golden brown.
08 - Let the baked apples cool for a few minutes, then drizzle with additional maple syrup. Serve warm, optionally accompanied by vanilla ice cream or Greek yogurt.