Rinse, then dice the unpeeled apples.
Microwave the diced apples with 2 tablespoons of water in a covered, microwave-safe bowl for 2 to 4 minutes, until the apples are lightly softened.
In a small bowl or mug, stir together the sugar and cornstarch, then stir in the vanilla. Set aside.
To a greased 10-inch bundt pan: add the frozen rolls and give the pan a little shake so they cover the bottom. Use a slotted spoon (or drain the apples) to add the apples over top of the rolls.
Sprinkle the brown sugar and cinnamon over top of the apples and rolls, then drizzle the vanilla mixture and melted butter overtop. These will drizzle downward and between the rolls as they rise, no need to stir.
Cover with a damp cloth or loosely cover with plastic wrap and let sit, at room temperature, up to 8 hours or overnight, until the rolls have risen near the top of the pan. That’s it, you’re done! Put up your feet and relax, you deserve it!
Once risen, bake the cake 350°F for 25 to 30 minutes (internal temperature 190°F to 200°F), until lightly firm when pressed and golden brown. Let the cake sit for 5 minutes or so, then turn out on a serving plate.