Preheat the oven to 350°F.
Arrange the apple halves, cut-side up, in a baking dish. Use a spoon or small melon baller to scoop out the cores and create a small well in the center of each apple.
Spread a little Challenge Spreadable Butter with Extra Virgin Olive Oil over the cut surface and inside the center of each apple.
In a medium bowl, combine the chopped nuts, brown sugar, maple syrup, cinnamon, nutmeg, cardamom if using, vanilla, salt, and remaining butter. Stir until evenly combined.
Spoon the nut mixture generously into the center of each apple half.
If using the cornstarch, whisk it into the 1/2 cup water until smooth. Pour the water mixture into the bottom of the baking dish around the apples.
Cover loosely with foil and bake for 20 minutes.
Remove the foil and continue baking for another 20 to 25 minutes, or until the apples are tender and the filling is golden and caramelized.
Spoon the buttery sauce from the bottom of the baking dish over the warm apples.
Serve warm with whipped cream or vanilla ice cream.