Melt the butter in a medium saucepan over medium heat, then stir in the brown sugar, salt, and heavy cream until fully blended. Bring it to a boil, then reduce the heat and let it simmer for 4 to 5 minutes, scraping down the sides so nothing sticks. Remove from heat and stir in the vanilla, pumpkin puree, and cinnamon, then set the sauce aside to cool a bit.

In a medium bowl, combine the chopped dates, melted butter, baking soda, and baking powder. Pour the boiling water over the top, stir, and let it sit for 20 minutes so the dates soften completely. Once they're soft, mash the mixture lightly with a fork until it turns into a chunky paste.

While the dates are softening, whisk together the flour, cinnamon, pumpkin spice, and salt in a separate bowl. Set this aside for later. Keeping the dry ingredients separate helps everything blend evenly once combined with the wet mixture.

In a large mixing bowl, stir together the pumpkin puree, sour cream, brown sugar, molasses, oil, eggs, and vanilla until smooth. Add the softened date mixture and mix until fully incorporated. The batter will look rich and dark at this point, which is exactly what you want.

Add the flour mixture into the wet ingredients and fold gently with a spatula until just combined. Overmixing at this stage can make the cake dense instead of light, so stop as soon as you don't see dry streaks. Pour the batter into your prepared, parchment-lined pan.

Preheat your oven to 350°F and bake the cake for about 55 minutes, or until a toothpick comes out clean or with a few moist crumbs. Every oven runs a little differently, so start checking around the 50-minute mark. Let the cake cool in the pan for 10 to 15 minutes before moving to the next step.

Use a skewer or the end of a wooden spoon to poke holes all over the warm cake. Pour about two-thirds of the pumpkin butterscotch sauce over the top and let it soak in for a few minutes. Slice into squares, drizzle with the remaining sauce, and serve warm.