Preheat oven to 350°F/180°C. Coat bundt pan with butter.

In a large bowl sift together flour, baking soda, baking powder, salt, cinnamon, nutmeg, and ginger. Set aside.

In a mixer bowl fitted with paddle attachment, or using a hand-held mixer, beat together eggs and brown sugar on medium-high speed until light and creamy, about 3 minutes. On low speed and with the mixer running, add oil slowly and beat until combined. Beat in vanilla extract and buttermilk until combined. Add flour mixture in thirds until just combined and turn off mixer. Fold in carrots and ½ cup of pistachios by hand until combined.

Pour batter into the prepared pan. Bake for 45-50 minutes on center rack until a toothpick inserted into the cake comes out clean. Allow bundt cake to cool 30 minutes in the pan on a wire rack. Then flip over the pan, tap gently in the top and sides to release the cake. Remove pan and let the cake cool completely on the wire rack.

Frost the top and sides of the cake once it has cooled, about 2 hours. Decorate with the remaining ½ cup of pistachios.

Frosted bundt cake can be kept in an airtight container in the refrigerator for up to 4 days.