Mix the cakeCombine yellow cake mix, pumpkin purée, brown sugar, and pumpkin pie spice until smooth.
Bake and pokeBake at 350°F (175°C) for 25 minutes. Cool 15 minutes, then poke holes across the surface with the handle of a wooden spoon.
Soak with sweetnessPour sweetened condensed milk evenly over the cake. Chill in the fridge for 30 minutes.
Top and drizzleSpread whipped topping over the chilled cake. Sprinkle toffee bits, then drizzle with caramel sauce.
Chill againRefrigerate at least 3 hours (or overnight) to allow flavors to meld and the topping to set.