Lightly brush the bottoms and sides of two 8-inch or 9-inch round cake pans (or 9 X 13-inch pan) with oil, or spray with non-stick baking spray. Line the bottoms with parchment paper rounds and set aside.: You will notice the pan surface glinting slightly where the oil clings, that sheen prevents sticking and helps the cake release cleanly. Lining the bottoms with parchment rounds creates a flawless circle when you invert the layers, and prevents tearing. One common mistake is skimping on the spray or parchment, which can lead to cake edges sticking and breaking, so be thorough and press the parchment into the pan to avoid air pockets.
First, brown the butter for your frosting. Add one stick of unsalted butter to a medium sized saucepan and heat over medium. Cook for about 3 minutes or until browned and fragrant (it will smell nutty), swirling the butter and stirring occasionally (be sure to scrape the sides and bottom of the pan to release all the brown bits that might have gotten stuck). Once browned, remove from heat and pour into a mixing bowl. Let it cool and solidify while you make your cake.: As the butter heats in a medium saucepan it will melt, foam, and then slowly darken with tiny brown flecks settling at the bottom. The aroma transforms from creamy to nutty, almost like toasted almonds, and that scent is the cue to remove it from heat. Pouring the browned butter into a bowl to cool lets it solidify slightly so it blends seamlessly with softened butter and cream cheese later. Overcooking is a risk, it can go from browned to burnt quickly, so watch closely and swirl the pan to avoid scorching.
Preheat the oven to 350°F. In a large mixing bowl (or in the bowl of a stand mixer), whisk the sugars and eggs together until the mixture is thick and lighter in color, 5-6 minutes. While mixing, slowly add the oil to the eggs and sugar until blended and smooth then add the buttermilk and vanilla.: You should hear the oven click as it reaches temperature and the interior light will glow, setting the stage for even baking. Whisking the sugars and eggs until thick and lighter in color incorporates air which contributes to a tender crumb. When you slowly add the oil while mixing, it emulsifies into the eggs producing a smooth, glossy batter. A common oversight is not fully preheating the oven, which can cause the cake to bake unevenly, so wait until it's fully up to temperature before placing pans inside.
In another bowl, whisk the dry ingredients together. If adding nuts, add them to your dry ingredients now, tossing to coat. Gradually add the dry ingredients to the wet mixture in three additions, mixing between each addition and scraping down the sides and bottom of the bowl to ensure everything is evenly mixed. Gently fold in the carrots (and raisins, if using), making sure there are no remaining pockets of dry ingredients.: Combine the flour , baking powder, baking soda, salt, and spices until evenly distributed and fragrant; you should smell the cinnamon and ginger blend. If you are using nuts or raisins, tossing them with a bit of flour before adding helps them distribute without sinking. Gradually adding the dry mix to the wet in three additions prevents over mixing, preserving a tender texture. A typical mistake is dumping all the dry ingredients in at once and over beating, which tightens the gluten and yields a dense cake.
Divide the batter between two prepared cake pans (or your 9 X 13-inch pan). One trick I like for even cake layers is to place each pan on my kitchen scale, zero it out, and then add half the batter. Do the same with the other pan and add a bit more as needed so they weigh the same. Bake for 35-40 minutes for 8-inch cake pans, for 9-inch cake pans or a 9 X 13-inch pan bake for 30-35 minutes or until a tester inserted in the centers comes out clean and the sides of the cake pull away from the edges of the pan. Cool for 10 minutes in the pans then run a knife around the edges of the cake pans and carefully invert the cakes on a cooling rack to cool completely.: You will see the batter change from loose to thick and cohesive, and scraping prevents pockets of flour that bake into dry streaks. Folding gently at this stage guards against deflating the mixture, keeping the crumb light. Avoid using high speed or vigorous stirring here, as that can overdevelop the gluten and create a tough texture.
While the cake cools, make your frosting. In the bowl of a stand mixer, combine the cooled 8 tablespoons of browned butter with the remaining stick of softened butter. Beat until the butter is light, smooth, and well blended. Add the cream cheese and salt then continue beating on medium to medium-high speed for about 3 minutes, scraping down the sides and bottom of the bowl to ensure everything is incorporated and there are no lumps. Add the maple syrup and vanilla and then the powdered sugar (1 cup at a time), beating until the frosting is smooth, whipped, and fluffy. Set aside until ready to use or refrigerate for up to 1 week if making it in advance.: Once the dry ingredients are fully incorporated, the grated carrots are folded in to distribute moisture and flecks of orange throughout the batter. The batter should look studded with carrot strands and hold together without streaks of flour. If you over fold, you risk compressing the batter which reduces rise; fold only until the carrots are evenly dispersed.
Place a heaping cup of icing on the first cake layer and use an offset spatula to spread it out. Top with your second layer and another heaping cup of icing, spreading down the sides and covering the whole cake. Note: Depending on how much icing you’d like on your cake, you may have 1/4 – 1/2 cup extra icing leftover.: To get even layers, I weigh each pan while adding batter so the layers match; visually you want similar heights for balanced baking. Place the pans on a center rack in the preheated oven and bake until a tester comes out clean and the sides pull away slightly from the pan. Rushing to open the oven or moving pans too soon can cause the cakes to sink, so resist peeking during the crucial middle of baking.
Bake for 35 to 40 minutes for 8 inch cake pans, for 9 inch cake pans or a 9 X 13 inch pan bake for 30 to 35 minutes or until a tester inserted in the centers comes out clean and the sides of the cake pull away from the edges of the pan: During baking, the aroma will grow and the top will turn a warm golden brown while the center springs back gently when touched. Use a thin toothpick or cake tester; if it comes out with moist crumbs, it is done, and if it has wet batter, give it a few more minutes. Opening the oven too often can lower the temperature and cause uneven rise, so check only near the end of the suggested time window.
Cool for 10 minutes in the pans then run a knife around the edges of the cake pans and carefully invert the cakes on a cooling rack to cool completely: The cake will continue to set as it cools and slightly pull away from the pan edges, and this resting prevents crumbling when you remove the layers. Inverting onto a rack helps air circulate so the bottom does not become soggy. A common error is trying to frost while the cake is still warm, which melts the frosting and creates a messy finish, so allow it to cool fully.
While the cake cools, make your frosting: Combine the cooled 8 tablespoons of browned butter with the remaining stick of softened butter and beat until light and smooth; the texture should become pale and fluffy. Adding the cream cheese and salt and beating for several minutes yields a silky, lump free base; scraping the bowl ensures even mixing. Then add the maple syrup , vanilla, and the powdered sugar gradually, beating until the frosting is whipped and airy. If the frosting is too loose, chilling briefly firms it; if too stiff, beat in a teaspoon of milk or adjust with gentle mixing.
Place a heaping cup of icing on the first cake layer and use an offset spatula to spread it out: Spread the frosting evenly so the first layer is supported, then top with the second layer and another heaping cup of icing, covering the sides and top. Aim for a smooth finish or rustic swirls, both look beautiful; if you prefer more frosting, this recipe can yield a little extra. One mistake is using cold frosting which resists spreading; ensure it is soft enough to spread smoothly without tearing the cake layers.