Brown Butter Carrot Sheet Cake with Brown Butter-Cream Cheese Frosting

Step 1
Place butter in a light-colored saucepan over medium heat. Cook, swirling the pan constantly, until butter is bubbling, smells nutty, and browned bits begin to form on the bottom of the pan, 5 to 10 minutes. Immediately remove from heat and pour butter into a heat-safe bowl. Allow brown butter to cool to room temperature, about 15 minutes.

Step 2
Preheat the oven to 325 degrees F (165 degrees C). Grease a 12×16-inch pan and line with parchment paper.

Step 3
Whisk together flour, baking soda, baking powder, cinnamon, allspice, nutmeg, and salt in a bowl.

Step 4
Beat cooled brown butter and brown sugar in a large bowl with an electric mixer on medium speed until well combined. Beat in eggs, one at a time, mixing well after each addition, until mixture is light and fluffy. Mix in vanilla. Pour in 1/2 of the flour mixture and mix until just combined. Add in remaining flour mixture and mix until just combined.

Step 5
Fold in shredded carrots, walnuts, and raisins. Pour batter into the prepared pan and smooth out the top with a spatula.

Step 6
Bake in the preheated oven until cake is golden and a toothpick inserted into the center of it comes out clean, 23 to 27 minutes. Transfer onto a wire rack and cool completely, about 30 minutes.

Step 7
While cake is cooling, repeat step 1 to brown butter for the frosting. Let cool to room temperature, about 15 minutes.

Step 8
Beat cream cheese in a large bowl with an electric mixer on medium-high speed until completely smooth. Add in cooled brown butter and mix until thoroughly combined. Mix in powdered sugar, 1 cup at a time, beating well after each addition. Mix in vanilla and salt. Beat frosting at medium-high speed until completely smooth, 1 to 2 minutes.

Step 9
Spread frosting over the cooled cake. Chill cake until ready to serve.