For the filling: coarsely grate the apples with their skins on.
Mix apples thoroughly with sugar, flour, lemon juice, cinnamon, and salt.
For the streusel topping: combine sugar, flour and salt; pressing out any lumps of sugar.
Then using your hands, rub in the butter until mixture is crumbly.
Spoon apple mixture into unbaked pie shell, then scatter streusel evenly over the top.
Bake in a preheated 400°F oven for 10 minutes, then reduce the temperature to 375°F and continue to bake for an additional 25-30 minutes until the filling is bubbly and the streusel topping is dappled with brown.
Remove pie from oven and let cool for 20-25 minutes before cutting.