Preheat oven to 375 degrees.
Butter your skillet or pan for baking.
Mix your sliced nectarines, sugar, cornstarch, and lemon juice in a bowl.
Pour the nectarines into your prepared pan.
In another bowl, mix your all-purpose flour, whole wheat flour, brown sugar, baking powder, and salt.
Pour in the melted butter and milk. Mix until it is almost smooth.
Pour and spread over the top of the nectarines.
Sprinkle with the 1 tablespoon granulated sugar.
Place in then oven and bake for 30-45 minutes.
You want the top to be lightly golden and the nectarines tender.
As a note, your nectarine juices might bubble over. This will depend on how much liquid is in your nectarines. If this starts to happen, or you want to prevent it from happening, place a sheet pan on the shelf beneath it.
Now, sit back and enjoy. You deserve it!