For the filling: Preheat the oven to 350 degrees F. Butter a 9-by-13-inch baking dish.
In a large bowl, combine the nectarines and blueberries. Add the granulated sugar, cornstarch, salt and orange juice and mix gently. Pour the fruit mixture into the prepared baking dish.
For the topping: In a large bowl, add the flour, oats, granulated sugar, brown sugar and salt and mix to combine. Cut 1 1/2 sticks of the butter into cubes, then cut the butter cubes into the flour mixture using a pastry cutter or 2 knives. Stir in the pecans and the reserved orange zest.
Spread the topping over the fruit. Cut the remaining 1/2 stick butter into cubes and dot the top of the crisp with it. Cover with foil and bake for 30 minutes. Uncover and continue cooking until the top is browned and the fruit is bubbling, 25 to 30 minutes. Let cool a bit before serving.
For the whipped cream: Mix the cream and granulated sugar in a bowl and whip to the desired consistency.
Plate the crisp into individual bowls and top with the whipped cream.