Prepare the oven and dish: Preheat your oven to 425°F / 220°C. Lightly butter a baking dish that's large enough to hold the 4 apples without them touching.
Prep the apples: Peel the top third of the skin from each apple.
Using an apple corer or a small paring knife, carefully remove the core, creating a hollow center but leaving the bottom intact.
Coat with syrup: Pour the maple syrup into a small bowl.
Roll each cored apple in the syrup, ensuring it's coated inside and out.
Place the apples upright in your prepared baking dish and set aside the remaining syrup.
Mix the filling: In a separate small bowl, combine the chopped walnuts, raisins, cinnamon, allspice, and nutmeg.
Stir in 1 tablespoon (15 ml / 0.5 fl oz) of the reserved maple syrup, then mix in the egg white until everything is well combined.
Fill the apples: Spoon the walnut mixture evenly into the hollowed-out centers of each apple.
Add toppings and foil: Drizzle the remaining maple syrup over the apples.
Cut the cold butter into 4 small pieces and place one on top of each apple's filling. Lightly butter 4 small squares of aluminum foil and place one, butter-side down, over the top of each apple to prevent the filling from burning.
Bake: Pour the ¼ cup of water into the bottom of the baking dish.
Bake for 30-35 minutes, basting the apples occasionally with the pan juices. The apples are done when they are tender when pierced with a knife but still hold their shape.
Serve: Let the apples cool slightly.
Serve them warm, spooning any remaining syrup from the pan over the top.
Finish with a generous dollop of crème fraîche.
Don't over-bake! The apples should be tender enough to pierce with a knife, but not mushy. Over-baking can cause them to burst and lose their shape.
