Preheat the oven to 350 degrees F. Butter a 10-inch cast-iron skillet.
MAKE THE CAKE:
In a large mixing bowl, use an electric mixer to combine the sugar and butter until they are well mixed. Mix in the pumpkin, eggs and vanilla.
In a separate bowl, whisk together the flours, baking powder, salt, cinnamon, nutmeg and cloves. Add the dry ingredients to the wet ingredients and mix until combined. Add the buttermilk and mix until incorporated. Stir in the pecans (if using). Scrape the batter evenly into the prepared skillet and smooth the top. Bake 40 to 45 minutes, or until the center is set (a toothpick inserted into the center should come out clean). Let the cake cool completely in the skillet.
ADD THE GLAZE:
In a medium bowl, whisk together the powdered sugar, syrup and 1 tablespoon of milk. If the mixture is too thick, add another teaspoon or more of milk. It should be of thick "drizzling" consistency.
Drizzle the glaze onto the cake in the skillet. Save the extra glaze (in a covered container) to add extra drizzle to individual servings. If you're into adding sea salt, sprinkle it on top!