Step 1

Preheat oven to 350 degrees. Butter and flour a 14-cup angel-food cake pan. In a large bowl, whisk together flour, baking powder, baking soda, salt, cinnamon, and ginger. In another large bowl, using an electric mixer, beat butter and brown sugar on medium-high until light and fluffy, 4 minutes. Beat in eggs, one at a time, scraping down bowl as needed. In a medium bowl, whisk together buttermilk and pumpkin puree. With mixer on low, add flour mixture to butter mixture in three additions, alternating with 2 additions pumpkin mixture. Scrape down bowl as needed. Fold in carrots and walnuts.

Step 2

Spread batter into pan, using a small spatula to fill any air pockets. Smooth top and firmly tap pan on a flat surface several times to remove air bubbles.

Step 3

Bake until a wooden skewer inserted in center of cake comes out clean, 70 to 75 minutes. Let cool completely in pan on a wire rack. Remove cake from pan. To serve, spoon glaze over top.