Preheat oven to 400° and lightly spray a 13 x 9 baking dish.
In a medium mixing bowl, whisk together flour and brown sugar.
Add 1 cup of butter into flour mixture (cut the cold butter into small pieces. Makes it easier to crumble), and using a pastry cutter or a fork, or two knives, mix until crumbly.
In a small bowl, whisk sugar, salt, nutmeg, cinnamon and corn starch together, set aside.
Rinse blueberries and nectarines. Slice each nectarines into 8 slices, add fruit and orange juice to large mixing bowl.
Sprinkle sugar mixture over fruit and stir until fruit is well coated.
Pour fruit mixture into prepared baking dish.
Add the remaining 1/4 cup butter (sliced) and just place on top of the fruit mixture randomly.
Add the flour mixture on top of fruit and spread evenly.
Bake uncovered at 400° for 50 minutes.
Serve warm with ice cream or whipped cream.