Preheat your oven to 350°F (175°C). Grease and flour a bundt pan to ensure easy removal of the cake.
In a medium bowl, whisk together the flour, baking soda, salt, and pumpkin spice. Set aside.
In a large mixing bowl, combine the granulated sugar, brown sugar, and melted butter. Beat until the mixture is smooth and creamy.
Add the eggs, one at a time, to the butter and sugar mixture, beating well after each addition.
Mix in the pumpkin purée and vanilla extract until fully incorporated.
Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk. Begin and end with the dry ingredients. Mix until just combined—do not overmix.
Pour the batter into the prepared bundt pan, smoothing the top with a spatula.
Bake in the preheated oven for 55-60 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for 10 minutes, then invert it onto a wire rack to cool completely.
Once cooled, dust the cake with powdered sugar or glaze with a simple icing if desired.