Preheat your oven to 375°F (190°C). In a large mixing bowl, combine 1 ¼ cups of all-purpose flour, ½ cup of cold unsalted butter, ¼ cup of sugar, and a pinch of salt. Mix until resembling coarse crumbs. Add ice water until dough holds together. Press into a pie pan and refrigerate for 30 minutes.

Remove the dough from the fridge and prick the base with a fork. Bake for 15 minutes until lightly golden. Let it cool.

In a bowl, toss 2 cups of sliced strawberries and 1 cup of blueberries with ¾ cup of sugar, 2 tablespoons of cornstarch, 1 tablespoon of lemon juice, and 1 teaspoon of vanilla. Let sit for about 10 minutes.

Pour the fruit mixture into the cooled pie crust, spreading evenly.

Mix 1 cup of oats, ½ cup of brown sugar, 1 teaspoon of cinnamon, and ¼ cup of melted butter until crumbly. Sprinkle over the berries.

Bake the pie for 30-35 minutes at 375°F (190°C) or until the topping is golden and filling is bubbly.

Cool on a wire rack for at least 1 hour before serving.