Meanwhile, heat butter in a saucepan and mix in the flour so that a paste forms.
Add water, both the sugars to the paste and let the mixture come to a boil.
Reduce the flame to low and let the sauce simmer.
Put the pastry crust on the mould and slice the apples.
Arrange the apples onto the crust and pour the sauce over the apples.
Now bake the pie for 15 minutes in the preheated oven after which reduce the temperature for 350°F and bake for another 30 to 40 minutes till the pie is ready.