With rack in the middle, preheat oven to 350ºF.

Line a jellyroll pan (14.19" x 9.25" or 17.25" x 12.25") with parchment paper.

In a medium bowl, whisk 1.5 cup flour, 1 teaspoon cinnamon, ½ teaspoon ginger, ¼ teaspoon nutmeg, 1 teaspoon baking powder, ½ teaspoon baking soda and ½ teaspoon salt.

In a standup mixer fitter with a whisk attachment (or hand-held mixer), on medium speed beat 1.25 cups sugar and 10 tablespoons butter until smooth, 3 minutes or so. Add 3 eggs, one at a time, beating well after each addition. Add 1 teaspoon vanilla.

Reduce speed to low, add shredded carrots.

Fold in the flour mixture. Add nuts.

Spread the batter on the jellyroll pan, smooth it out.

Bake 18-20 minutes, or until a toothpick inserted in the middle comes out clean. Turn the pan halfway through baking.

Transfer to a cooling rack and allow to cool completely in the pan.

In a standup mixer fitted with a whisk attachment, beat all the frosting ingredients on medium speed until smooth, a minute or so.

Turn speed up to medium high, and beat until frosting holds stiff peaks, about a minute. Do not overbeat!

Using a serrated knife, cut the cake in half crosswise, then cut each haft again to get four equal rectangular pieces.

Place one piece, top side down, on a serving platter. You can tuck pieces of parchment paper on the sides to keep the platter clean from frosting.

Spread ½ cup of frosting over the layer.

Place the second layer, top side up. If the edges are uneven, apply slight pressure to even it, or trim with a serrated knife. Spread another ½ cup frosting.

Repeat with a third layer, top side up, and another ½ cup frosting. Top with the fourth layer, top side up.

Spread about 1.5 cups of frosting on the sides of the cake to seal in the crumbs. Don't worry if there are crumbs in your frosting. Chill the cake in refrigerator for 15 minutes.

Spread the remaining frosting on the top and sides of the cake.

Refrigerate the carrot cake for at least 3 hours, and up to 12 hours.