Step 1: Bake the Crust
Preheat oven to 375°F (190°C).
Prick the crust with a fork to prevent bubbling.
Bake for 12–15 minutes, until lightly golden. Set aside.
Step 2: Mix the Crumb Topping
In a bowl, combine walnuts, flour, and brown sugar.
Add melted butter and mix with fingertips until crumbly. Set aside.
Step 3: Prepare the Apple Filling
In a large bowl, mix sugar, corn starch, and cinnamon.
Toss in sliced apples and lemon juice until evenly coated.
Step 4: Soften the Apples
Cover the bowl loosely with waxed paper or vented plastic wrap.
Microwave on high for 12 minutes, stirring halfway through.
Step 5: Seal the Crust
While apples are hot, brush the baked crust with beaten egg white.
This creates a moisture barrier to keep the crust crisp.
Step 6: Assemble the Pie
Spoon the apple filling into the crust and spread evenly.
Sprinkle the crumb topping generously over the apples.
Step 7: Bake to Perfection
Increase oven temperature to 425°F (220°C).
Bake for 10–12 minutes, until topping is golden brown.
Cool on a wire rack for at least 30 minutes before serving.