Mix berries, white sugar, and cornstarch together lightly. Set aside.
Cream brown sugar, butter, and vanilla extract together in a separate bowl. Mix in flour and cinnamon. Stir in oats just until mixed. Chill topping for 15 minutes.
Preheat the oven to 375 degrees F (190 degrees C).
Place berries in the bottom of a 9x9 inch baking pan. Place chilled topping on berries, pressing lightly.
Bake in the preheated oven until golden, about 1 hour.
Frozen Berry Crisp · Dinner Match Lab | Dinner Match Lab