• Preheat oven to 400 degrees.

Filling

• Combine the sugar and flour together in a medium mixing bowl. Add the sour cream, egg, vanilla, and salt. Beat with an electric mixer over medium speed for 5 minutes.
• Gently fold in the blueberries. Pour the batter into the pie shell.
• Bake for 30 minutes. You may need to lightly cover the pie edges with foil to avoid over-browning.

Streusel Topping

• While the pie is baking, prepare the topping. In a small bowl, add the flour and sugar and stir until combined. Add the cold butter and mix with a fork or pastry blender to incorporate the butter into the mixture to create a crumbly mixture.
• Remove the pie from the oven and sprinkle the streusel topping over the pie. Bake in the oven for 10 to 15 minutes or until the topping starts to turn golden.
• Allow the pie to cool before serving.
• Store in the refrigerator.