Spice Cake With Cream Cheese Frosting

1. Adjust oven rack to middle position and heat oven to 350 degrees. Grease 13 by 9-inch baking pan, line with parchment paper, grease parchment, and flour pan. Combine cinnamon, cardamom, allspice, cloves, and nutmeg in small bowl; reserve 1⁄2 teaspoon of spice mixture for frosting.
2. Melt 4 tablespoons butter in 8-inch skillet over medium heat, 1 to 2 minutes. Cook, swirling pan constantly, until butter is light brown and has faint nutty aroma, 2 to 4 minutes. Add spices and continue to cook, stirring constantly, 15 seconds. Remove from heat and let cool to room temperature, about 30 minutes.
3. Whisk flour, baking powder, baking soda, and salt together in medium bowl. In small bowl, gently whisk eggs, egg yolks, and vanilla to combine. Using stand mixer fitted with paddle, beat remaining 12 tablespoons butter with sugar and molasses on medium-high speed until pale and fluffy, about 3 minutes, scraping down bowl as needed. Reduce speed to medium and add cooled butter-spice mixture, ginger, and half of egg mixture; mix until incorporated, about 15 seconds. Repeat with remaining egg mixture; scrape down bowl. Reduce speed to low and add flour mixture in 3 additions, alternating with 2 additions of buttermilk, scraping down bowl as needed. Mix at medium speed until batter is thoroughly combined, about 15 seconds. Give batter final stir by hand.
4. Scrape batter into prepared pan, smooth top with rubber spatula, and gently tap pan on counter to release air bubbles. Bake cake until toothpick inserted in center comes out clean, 32 to 37 minutes. Let cake cool completely in pan on wire rack, about 2 hours. Run paring knife around edge of cake to loosen from pan. Invert cake onto wire rack, discard parchment, then turn cake right side up onto serving platter.
5. Stir reserved spice mixture into frosting. Spread frosting evenly over cake, sprinkle with walnuts, if using, and serve. (Cake can be refrigerated for up to 2 days. Bring cake to room temperature before serving.)

SPICE CAKE WITH ORANGE–CREAM CHEESE FROSTING
Add 1-1⁄2 teaspoons grated orange zest to frosting with vanilla. Substitute slivered almonds or coarsely chopped hazelnuts for walnuts.