Sift flour and salt together. In a small bowl, combine flour, warm water, and oil Stir to combine and turn out on to a work surface. Knead dough until smooth. Cover dough with a towel and allow it to rest for 1 hour.

Preheat the oven to 385 degrees F.

Divide dough into 5 or 6 equal pieces. Roll out one piece of dough on a floured surface until thin and about 6 to 7 inches square (or slightly rectangular). Spread a very thin layer of sour cream on the dough. Put about 1/2 to 3/4 cup grated apples on one end of the dough. Sprinkle the apples with 1 teaspoon of sugar. Roll up the dough beginning with the end with the apples. Pinch the dough to seal the ends and edges. Repeat process with each piece of dough.

Pour the melted butter in a 9 X 13-inch baking sheet. Place the strudels in the pan and roll them around to coat each one with butter. Bake for 40 minutes. Turn the oven to broil and broil for a few minutes to lightly brown the top of the strudels. (Do not walk away, they will burn very quickly).

Remove the strudels from the oven. Set the temperature to the oven back to 385 degrees F.

Pour the hot milk over the strudels. Return pan to the oven and bake for 3 minutes until milk has been absorbed and/or evaporated. Remove strudels from the oven and allow to cool in the pan for about 10 minutes. Transfer strudels to serving plates and serve warm with vanilla sauce.

In a medium bowl, whisk together sugar and flour. Add eggs and egg yolk and whisk to combine. Whisk in the heavy cream and half-and-half. Transfer the mixture to a saucepan. Cook over medium heat, stirring constantly, until mixture starts to thicken and just before it reaches a simmer. Remove pan from heat. Stir in the vanilla and pour the mixture into a bowl. Press plastic wrap to the surface of the sauce to prevent a skin from forming. Serve warm or at room temperature.

If the sauce becomes too thick, stir in hot milk, 1/4 cup at a time until desired consistency.