Preheat oven to 375°F

Place blueberries in a 2 quart square baking dish. Sprinkle with lemon juice, or the orange juice/white vinegar combination.

In a separate bowl, combine brown sugar, flour, oats, cinnamon and salt. Using a pastry blender (or two knives) cut in butter until the mixture resembles coarse crumbs. It's ok towards the end of blending to use your hands to break down the butter further. Only be careful that the heat from your hands doesn't make the butter too soft. Sprinkle evenly over blueberries.

Bake in 375°F oven for 25-30 until the top is golden brown and berries are oozing their juice.