Start by preheating your oven to 350°F so it's fully heated by the time your batter is ready. Spray a 9x13-inch pan generously with non-stick cooking spray, making sure to coat the corners. I sometimes line the pan with parchment paper too, just for easier cleanup later.
In a large bowl, combine the cake mix, pumpkin puree, eggs, oil, water, pumpkin pie spice, and cinnamon. Beat everything together with an electric mixer until the batter looks smooth and there are no dry streaks left. It should be thick but pourable, similar to a regular cake batter.
Pour the batter into your prepared pan and spread it out evenly with a spatula. Bake for 28 to 32 minutes, or until a toothpick inserted in the center comes out clean. Keep an eye on it near the end so the edges don't overbake while the middle finishes.
Once the cake comes out of the oven, let it sit for about 10 minutes so it's warm but not piping hot. Using the handle of a wooden spoon or a thick straw, poke holes all over the top, spacing them about an inch apart. Go about two-thirds of the way down so the filling has somewhere to settle.
Slowly pour the sweetened condensed milk over the entire cake, focusing on the holes you just made. Let it sit for a minute so the milk has time to sink in before you move on. You'll notice the cake already starts looking richer and darker in color.
Warm the caramel sauce slightly so it's pourable, then drizzle it over the same holes. This second layer is what makes the cake so wonderfully moist all the way through. Let the cake cool completely at room temperature before adding any toppings.
Beat the softened cream cheese and powdered sugar together until smooth and fluffy with no lumps. Gently fold in the whipped topping by hand so you don't deflate all that airiness. This topping should be light, spreadable, and just a little tangy.
Spread the cream cheese topping evenly over the cooled cake using a spatula. Sprinkle the toffee bits over the top, and add an extra drizzle of caramel if you like things extra sweet. Cover the pan and refrigerate for at least 3 hours before serving.