Preheat your oven to 350° F. This is crucial for getting that perfect golden crust.
If you're using a frozen pie crust, remove it from the freezer and let it sit at room temperature. If you opted for a homemade crust, keep it refrigerated until it’s ready to fill. You want it to be nice and chilled when it hits the oven.
In a large mixing bowl, combine the frozen mixed berries, vanilla extract, granulated sugar, and flour. Stir gently until the berries are well coated with the mixture. This step ensures that the filling is sweetened perfectly and thickened slightly.
Carefully pour the berry mixture into the pie crust. Use a spatula to even out the top, ensuring that the berries are evenly distributed for consistent flavor in every slice.
In another separate mixing bowl, measure out the ingredients for the streusel: flour, rolled oats, granulated sugar, brown sugar, butter, and salt.
Using your hands, mix the streusel ingredients together. You want it to come together, incorporating the butter throughout until everything resembles moist sand. This is where the magic happens, transforming simple ingredients into a crunchy topping.
Spread about 3/4 of the streusel evenly over the berry mixture in the pie crust. This topping will bake up beautifully, creating a crispy contrast to the soft berries.
Place the pie in the preheated oven and bake for about 1 hour. Keep an eye on it; you’re looking for a golden-brown crust and topping. The berries will bubble up, showcasing their gorgeous colors.
Once baked, remove the pie from the oven and let it cool completely before cutting into it. Patience is key here, as slicing into a hot pie can make a mess!
Enjoy your Mixed Berry Streusel Pie with a scoop of vanilla ice cream or a dollop of whipped cream for that ultimate treat experience.
