Preheat your oven to 375°F (190°C).
In a saucepan over medium heat, combine frozen mixed berries, granulated sugar, lemon zest, lemon juice, and a splash of water. Allow it to simmer, stirring occasionally as the berries melt and the mixture thickens into a syrupy consistency.
In a separate bowl, mix together flour, melted butter, milk, sugars, and vanilla until the crumble topping forms. Set aside.
Let the berry compote simmer for about 20 minutes, then stir in a cornstarch slurry to thicken the sauce. Once it thickens, remove from heat and let it cool slightly.
Pour the berry compote into an oven-safe baking dish, then evenly sprinkle the crumble topping over the berries.
Bake for 40-45 minutes, or until the topping is golden brown and cooked through. Allow it to cool for 5 minutes.
Serve warm with a scoop of Breyers natural vanilla ice cream and enjoy!
