Put a few ice cubes in a cup and add a little water. Set aside.

Place flour, sugar, and salt in the bowl of a food processor with the knife attachment. Pulse to combine. Turn processor on and add margarine. Process just until coarse crumbs form. Add the egg and water (from the cup with ice cubes) slowly, just until dough comes together. Divide dough in half. Freeze half for later.

Roll out dough to a large circle. Carefully invert onto a 9–10-inch deep pie pan. Press down evenly and trim edges. Set aside.

Preheat oven to 400 degrees Fahrenheit (200 degrees Celsius).

Heat oil for filling in a wok or large frying pan. Add apples and rest of filling ingredients. Cook over medium/high heat for approximately seven minutes, stirring occasionally, until apples are evenly coated and beginning to soften. Cool slightly.

In a medium bowl, combine all custard ingredients and whisk together well.

Place apples in prepared crust. Pour custard over the apples, but do not overfill. Depending on how deep your pan is, you might have a little extra. (Add to any sweet kugel or freeze for later use.)

Place pie pan on a sheet of foil or a baking sheet and slide into the oven. Bake for 20 minutes or until top is golden.

If it starts to turn brown, cover loosely with a piece of foil or parchment paper.

Meanwhile, combine all streusel ingredients in a small bowl.

After 20 minutes, remove pie from oven and sprinkle with streusel topping. Lower temperature to 350 degrees Fahrenheit (180 degrees Celsius) and continue baking for 15–20 minutes.

Cover crust edges with foil so it doesn’t burn.

Serve warm with (parve) vanilla ice cream if desired.