Preheat oven to 375 degrees. Using a cylindrical apple corer, core apples three-quarters of the way down. Fit snugly in an ovenproof skillet or a loaf pan.
Stir together sugar, butter, nuts, vanilla seeds, and salt in a small bowl. Divide sugar mixture among apples (about 2 teaspoons each). Sprinkle with nuts. Bake until apples are soft, about 1 hour. Serve warm with pan syrup spooned on top.