Preheat oven to 350°F. In a large bowl, meat together the sugar and flour with cream, egg, vanilla, lemon juice and zest, and salt.
Add blueberries and gently fold. Pour filling into prepared pie crust and bake 40 minutes.
While pie bakes, make the topping but cutting the butter into the flour and sugar until crumbly. Sprinkle over pie and continue baking for 20-30 more minutes until center is set.