Turn your oven to 350°F. Prepare a 9×5-inch loaf pan by greasing and flouring it, or line it with parchment paper.

In a medium mixing bowl, sift together the flour, baking powder, baking soda, salt, and pumpkin spice using a fine-mesh sieve or sifter.

In a large mixing bowl, beat the eggs with a balloon whisk until slightly frothy. Gradually add the sugar while whisking until pale and thickened. Add the vanilla, vegetable oil, buttermilk, and butternut squash puree. Whisk or use a hand mixer on low speed until smoothly combined.

Using a silicone spatula, gently fold the dry ingredients into the wet mixture. Stir just until no flour streaks remain. Don't overmix.

Transfer the batter to the prepared loaf pan and smooth the top with the back of a spoon or an offset spatula. Bake for 60–70 minutes, until a toothpick or cake tester inserted in the center comes out clean. A digital oven thermometer helps ensure accurate baking temperature.

Set the pan on a wire cooling rack and let the loaf cool completely in the pan before icing.

Make the icing: In a small bowl, combine the icing sugar, maple syrup, and pumpkin spice using a mini whisk or regular whisk. Start with 1 tablespoon of syrup and add more until you achieve a pourable consistency.

Drizzle the icing over the cooled loaf and add an extra pinch of spice if desired. Let the icing set briefly before slicing.