Preheat oven to 375°F (190°C). Grease a 9-inch pie dish or an 8x8 inch baking dish.
In a large bowl, combine mixed berries, granulated sugar, cornstarch, and lemon juice. Toss gently to coat the berries evenly. Pour the berry mixture into the prepared baking dish.
In a separate medium bowl, combine flour, rolled oats, brown sugar, and sliced almonds. Add the cold butter cubes. Use your fingers or a pastry blender to cut the butter into the dry ingredients until the mixture resembles coarse crumbs.
Evenly sprinkle the almond topping over the berry filling in the baking dish.
Bake for 35-45 minutes, or until the topping is golden brown and the berry filling is bubbling around the edges. If the topping starts to brown too quickly, you can loosely tent it with foil.
Let the crisp cool for at least 10-15 minutes before serving. Serve warm, perhaps with a scoop of vanilla ice cream or a dollop of whipped cream.
Notes
This berry almond crisp is incredibly versatile. Feel free to experiment with different berry combinations or add a pinch of cinnamon to the topping for extra flavor.