Brown Family's Favorite Pumpkin Pie

I saw this recipe in the All Recipes Holidays 2025 issue. Intriguing because I've not seen a pumpkin pie with a crumble before.

1 15oz can pumpkin puree
1 14oz can sweetened condensed milk
2 egg yolks
1 tsp ground cinnamon
½ tsp ground ginger
½ tsp ground nutmeg
½ tsp salt
2 egg whites
1 9" unbaked pie shell
2 tbsp all-purpose flour
¼ cup packed brown sugar
1 tsp ground cinnamon
2 tbsp butter, chilled
1 cup chopped walnuts

Preheat the oven to 425° F.
Mix pumpkin, sweetened condensed milk, and egg yolks in a large bowl until smooth. Stir in 1 teaspoon cinnamon, ginger, nutmeg, and salt until well combined.
Beat egg whites in a clean glass or metal bowl until soft peaks form, about 2 minutes. Fold egg whites into pumpkin mixture until no streaks remain. Pour filling into unbaked pie shell and smooth the top.
Bake in preheated oven for 15 minutes. Meanwhile, combine flour, brown sugar, and 1 teaspoon cinnamon in a small bowl until evenly blended. Cut butter into flour mixture until crumbly, about 2 minutes. Stir in chopped walnuts. Sprinkle topping over pumpkin pie.
Reduce oven temperature to 350°F.  Bake pie until center is set and a knife inserted near the center comes out clean, about 40 minutes. Cool pie on a wire rack until room temperature, about 2 hours.