Move the oven rack to the middle position and preheat oven to 350°F.
Place the frozen berries in a 9 x 13 Pyrex pan. Sprinkle the berries with the balsamic vinegar.
In a small bowl whisk together cornstarch and sugar. Sprinkle the mixture over the berries.
Use a spoon to toss the berries until the cornstarch is evenly distributed.
In a medium bowl make the topping by mixing together the oats, flour, brown sugar, and softened butter. Use your hands or a wooden spoon to mix everything together.
Crumble topping over the berries and bake for 45-50 minutes, rotating the pan half-way through cooking. The berry crumble is done when then topping is golden brown and the berry mixture nice and bubbly.
Cool 10-15 minutes before serving. This crisp is especially delicious served with a little bit of fresh whipped cream or ice cream.