Preheat the oven to 350°F.
Grease a bundt pan with oil or non-stick cooking spray then flour the pan. Tap out the excess and set the pan aside.
In the bowl of a stand mixer fitted with the batter blade (or in a bowl with an electric mixer) cream together the butter and sugar until light and fluffy. Scrape down the sides and add the eggs, one at a time, blending and scraping down the sides of the bowl after each addition. When the eggs are fully incorporated, blend in the pumpkin and vanilla. It may look curdly and horrid, but that's okay! Keep going!
In a separate bowl, whisk together the flour with the rest of the dry ingredients. Add about 1/3 of the flour to the butter mixture and blend until incorporated. Add 1/2 of the buttermilk and blend in completely. Repeat with another 1/3 of the flour and blend. Finish mixing the batter by adding the final 1/2 of buttermilk, mixing, then adding the final 1/3 of flour.
Spoon the cake batter into the prepared bundt pan, gently smooth the top and bake the cake for 30-40 minutes, or until a toothpick or skewer inserted in the thickest part of the cake comes out clean and the cake springs back when pressed lightly with your finger.
Transfer the pan to a cooling rack and let rest for 5 minutes before carefully turning out onto the rack to cool completely. While the cake cools, make the caramel...