Preheat oven to 350 degrees F and place rack in center of oven. Grease and lightly flour a 10 cup ( 9 x 2 1/2 inches/23 x 6 cm) bundt pan and set aside.
In a medium bowl whisk together the flour, baking soda, baking powder, salt, ground nutmeg and ground cinnamon. Set aside.
In the bowl of you electric mixer, beat the butter on high speed for about one minute, until smooth. Add all the granulated white sugar at once and mix until pale and fluffy, about 3 minutes. Add the eggs one a time, mixing well after each addition. Mix in the vanilla extract.
Fold the flour mixture into the batter and mix until just combined. Don't overmix. Fold in the grated carrots until just combined. This will be a thick cake batter.
Pour batter into prepared pan and bake between 45 - 60 minutes or until a toothpick comes out with a few crumbs.
Remove the cake from the oven and place on a cooling rack for 10 minutes. Invert the cake onto the cooling rack and release the baking pan. Leave cake to cool completely.
Make the glaze by combining the powdered sugar and milk in a medium bowl. Whisk until smooth.
Pour the glaze over the cooled cake. (see tips in the post). Top with chopped walnuts if using.
Cover and refrigerate any leftovers.
Slice and serve. Cover any leftovers.