Bake the Cinnamon Pie Crust

1. Preheat the oven to 350°F (175°C). Line a baking sheet with parchment paper.
2. Cut the pie crust into strips about 1 inch wide. Beat the egg with 1 teaspoon of water, then lightly brush the strips with the egg wash.
3. Arrange the strips on the baking sheet, leaving space between them. Bake for 14–16 minutes, or until golden and crisp.
4. Brush the baked strips lightly with the melted salted butter. Mix the granulated sugar and cinnamon, then sprinkle over the strips. Let cool completely before breaking into bite-sized pieces.

Cook the Apple Pie Filling

1. Peel, core, and dice the Granny Smith apples into ½-inch pieces.
2. Melt the unsalted butter in a skillet over medium heat. Add the apples and cook for about 5 minutes, stirring occasionally.
3. Stir in the brown sugar, cinnamon, and nutmeg.
4. Mix the cornstarch with ¼ cup cold water until smooth. Pour into the skillet and stir gently.
5. Cook for another 3–5 minutes, until the apples are tender and the sauce is thick enough to coat them. Remove from the heat and let cool until no longer hot.

Assemble the Sundaes

1. Divide half of the apple filling among four dessert cups. Add a few cinnamon pie crust pieces to each.
2. Add about 1 cup of vanilla ice cream to each cup.
3. Spoon the remaining apple filling over the ice cream and finish with the remaining pie crust pieces. Serve immediately.