Using a food processor, add graham crackers and pulse into finely ground.
Add brown sugar; pulse until well combined.
Add melted butter; pulse until well combined.
Spray a 9-inch pie plate with nonstick cooking spray. Transfer graham cracker mixture into pie plate. Using a flat-bottomed glass, press mixture into bottom of pie pan and up sides.
Bake for 13-15 minutes, or until crust is light golden brown.
Remove pie pan from oven and place on a wire rack to cool.
For the Blueberry Filling
Using a large bowl, add sugar, flour, eggs, sour cream, lemon juice and vanilla extract; whisk together until well combined.
Spread blueberries evenly into the cooled pie crust.
Pour cream mixture over blueberries.
For the Crumb Topping
Increase oven temperature to 350°F.
Using a medium bowl, add all of the ingredients for the topping; stir with a fork until a crumbly mixture forms.
Sprinkle crumb topping evenly on top of pie.
Bake for 50-55 minutes, or until crumb topping is light golden brown. (Note: Check pie after ~40 minutes. If necessary, top with foil to prevent burning.)
Place pie on wire rack and let cool for 30-45 minutes before serving.
{Optional} Dust top of pie with powdered sugar before serving.
{Optional} Serve with a scoop of vanilla ice cream.
Notes
Can substitute for a store-bought graham cracker pie shell.