Pre Heat oven to 350 degrees, and butter and flour a 12-cup (or larger) capacity bundt pan.
In a medium bowl, whisk the flour, baking powder, baking soda, salt, cinnamon, nutmeg, allspice and ground ginger until well combined.
In the bowl of a stand mixer fitted with the paddle attachment, combine brown sugar, butter and olive oil. Beat on medium-high until light and fluffy, about 3 minutes. Add the eggs one at a time, mixing for about 20 seconds in between each egg. Add the pumpkin purée and sour cream, and mix until well combined, scraping the bottom and sides of the bowl as necessary.
Remove the bowl from the mixer, and use a rubber spatula to fold in the dry ingredients until well combined. Make sure to scrape the bottom and sides of the bowl to ensure an evenly mixed batter.
Pour the batter into the prepared bundt pan, smoothing out the top and tap the pan on the countertop a few times to release any large air bubbles.
place cake in the oven and bake the cake until golden and puffed, and a tooth pick inserted into the center comes out clean, 55 to 65 minutes. The baking time may vary depending on your oven, so keep an eye on it.
Allow the cake to cool in the pan for about 10-15 minutes. Then, carefully invert it onto a wire rack to cool completely.
once the cake is cooled begin working on the glaze by combining all the ingredients in a small bowl and mix until combined.
note: if glaze is too thick add more milk
drizzle glaze over cake and top with freshly grated nutmeg and toasted pistachios or pepitas (pumpkin seeds), if desired.
