Preheat oven to 375˚F.
Wash and dry berries. (Berry proportions can vary but should total about 7 cups.)
Immerse whole berries in bowl of water. Gently swish in water, drain, rinse and drain again. A salad spinner works well for this. Then place berries in a single layer on a shallow pan lined with double thickness paper towels and gently blot to remove excess moisture.
Place berries in 7x11x2-inch (2 quart) glass baking dish.
Sprinkle 1 tablespoon of balsamic vinegar evenly over the berries. It will intensify the flavor of the berries.
Combine sugar and corn starch and sprinkle over berries. Gently toss berries and sugar mixture.
Put flour, sugars and baking powder in a food processor bowl. Pulse to combine. Add butter cubes and pulse until mixture forms coarse clumps. Add nuts and pulse briefly, leaving coarse chopped pieces. (If Food Processor is not available, topping could be combined with a fork or pastry blender and nuts chopped with a knife and stirred in.)
Sprinkle topping evenly over berries. Bake for 35 to 40 minutes or until the fruit is bubbling and the topping has browned.
Serve warm or cold in bowls topped with whipped cream or ice cream.
It’s delicious served warm or cold. If totally cooled before serving, it will be less runny. For an elegant idea to serve warm, try baking and serving it in eight 8 oz-sized or ten 6 oz-sized ramekins.