SourCream Dutch Apple Pie

At Thanksgiving this pie was a big hit.
It is very rich and the calories are huge for 1 serving 624!
Waistline, what waistline!
When cooked this apple pie has a nice thick custard, the apples stay firmer,the pie presents well on a plate.
This makes a very big deep pie.
Really could serve 10 easily tho recipe says 8 servings.

1 9 1/2 inch deep dish pie shell (whatever pie crust is your favourite)mine is from Tenderflake lard box.
Filling:
1 1/4 cups full fat sourcream
3/4 cup sugar, I used half white and brown
1 large egg
1/4 cup all purpose flour
1/4 tsp. salt
2 tsp. vanilla extract
7-8 cups peeled cored thinly sliced apples , I used 8 cups of
Spys but any baking type apple, Granny Smiths etc is fine
Streusel:
1 cup all purpose flour
1/2 cup sugar, white
1/2 cup brown sugar, firmly packed
1 tsp. cinnamon
1/4 tsp. mace, nutmeg each ,optional
pinch of salt
6 TBSP. butter
3/4 cup walnuts, chopped,optional ,I did not use nuts in mine.
Place the prepared pie shell in freezer for 15 minutes, preheat oven to 400.
In large bowl , whisk the sour cream, sugars, egg, flour salt, and vanilla til well blended.
Add apples, stirring til apples are well coated with sour cream mixture.
Turn filling into pie shell, smooth top laying the apple slices down.
Place pie in oven, bake for 15 minutes, decrease oven to 350,bake for 30 minutes.

Struesel topping: in a large bowl combine flour, sugars, cinnamon, mace, nutmeg, salt and walnuts if using.Add in the butter, stir with a fork , then use your fingers to rub the mixture until it becomes a uniform crumb like texture.
Remove pie from oven , carefully top with the streusel , spreading it evenly over apples.Return pie to oven and bake for 15 - 20 minutes more til golden brown .
Wait 2 hours before serving.
You can serve this chilled but I prefer it warm .
Can be made the day before and kept in the refrigerator.
My Mom suggested this would make an excellent pie using rhubarb instead of apples.