Heat oven to 350°F. Grease three 8-inch cake pans; line bottoms with parchment and grease again.
Sift flour, baking soda, spices + salt. Beat eggs, sugar, oil, buttermilk, zest + vanilla until smooth. On low, gradually add dry ingredients just until combined. Fold in carrots, pineapple, coconut + walnuts.
Divide among pans. Bake 35-45 min, rotating halfway, until a toothpick comes out clean. Cool in pans 10 min; turn onto racks set over a baking sheet.
Glaze: Melt butter over medium heat until golden brown + nutty. Reduce heat; carefully stir in sugar, buttermilk, honey + baking soda. Bring to a boil over medium-high; cook, stirring often, until deep caramel color. Evenly pour over warm cakes; cool completely.
Frosting: Beat butter + cream cheese until smooth, about 3 min. Beat in vanilla. With mixer off, add sugar ½ cup at a time, mixing on low after each addition. Beat medium-high 30 sec.
Evenly frost each layer, then insert skewers to secure. Refrigerate 30 min. Apply final coat, remove skewers, then smooth over holes. Garnish with coconut + walnuts.
