Preheat oven to 350°F (175°C). Grease a 9×13-inch baking dish.
- In a large bowl, mix together the cake mix, pumpkin purée, eggs, and milk or water (as directed on the box), plus pumpkin pie spice if using. Stir until smooth.
- Pour the batter into the prepared baking dish and bake for 25–30 minutes, or until a toothpick inserted in the center comes out clean.
- Let the cake cool for about 10 minutes. Use the handle of a wooden spoon to poke holes all over the surface.
- Pour sweetened condensed milk evenly over the warm cake, letting it soak into the holes.
- Cool the cake completely at room temperature.
- Spread whipped topping evenly over the cake.
- Drizzle with caramel sauce and sprinkle toffee bits on top.
- Chill in the refrigerator for at least 1 hour before serving. Serve cold or at room temperature.