Set the oven to 350°F. Prepare a 9x9x3" or 9x11x3" deep baking dish by spraying it with nonstick baking spray.

In a mixing bowl, cream together the granulated sugar, brown sugar, and butter for about 3 minutes until light and fluffy.

Add in the eggs, vanilla extract, buttermilk, maple syrup, and pumpkin puree. Mix until smooth.

In a separate bowl, whisk together the flour, baking powder, baking soda, kosher salt, and pumpkin spice. Gradually mix the dry ingredients into the wet ingredients until fully combined.

Pour the batter into the prepared baking dish. Bake for 45-55 minutes, or until a toothpick inserted into the center comes out clean and the cake no longer jiggles. The cake will be moist and dense.

Once done, remove the cake from the oven and allow it to cool.

While the cake bakes, prepare the toffee sauce. In a medium stockpot over medium-low heat, melt the butter and brown sugar together, stirring constantly for about 10 minutes until the mixture is well-combined.

Add in the heavy cream and vanilla extract, continuing to cook for another 5 minutes. Be sure not to let the sauce boil. If it begins to bubble, reduce the heat. The sauce should be silky smooth.

Once ready, transfer the sauce to a glass container to cool.

Once the cake has cooled, poke holes all over the top using a toothpick. Pour the toffee sauce over the cake, allowing it to soak in. Let the cake rest for at least 1 hour to absorb the sauce before serving.