Berry Crumble

Bahan-bahan (8 porsi)

• 1 teaspoon unsalted butter, (at room temperature)
• 5 cups frozen unsweetened mixed berries
• 1 tablespoon freshly squeezed lemon juice
• ⅔ cup granulated white sugar
• 2 tablespoons cornstarch
• 1 cup all purpose flour
• ⅔ cup packed dark brown sugar
• 1 teaspoon ground cinnamon
• ¼ teaspoon salt
• ½ cup (1 stick) cold unsalted butter, (cubed)
• vanilla ice cream, (for serving (optional))