Preheat oven to 350°F.
Unroll pie crust and place in a pie plate.
1 homemade*, refrigerated or frozen pie crust
In a large bowl, whisk together the sugar, flour, salt, eggs and milk; stir in the diced rhubarb.
1 1/2 cups sugar, 3 tablespoons flour, 1/4 teaspoon salt, 2 eggs, 2 tablespoons milk, 3 cups diced rhubarb
Pour the filling into the pie crust.
In another bowl, combine the dry ingredients for the topping. Then, add the butter and stir until it's crumbly.
1/4 cup sugar, 1/4 cup brown sugar, 1/2 cup flour, 1 teaspoon cinnamon, 1/4 cup butter
Sprinkle the crumb topping over the custard filling.
Bake the pie for 40 minutes, then cover with foil and bake an additional 10-15 minutes. The pie is done when the center of the custard filling is set (has very little jiggle).