Pumpkin Spice Layer Cake with Toasted Walnut Buttercream
3 cups all-purpose flour
2 teaspoons baking powder
1 teaspoon baking soda
1 teaspoon salt
1 tablespoon ground cinnamon
1 tablespoon ground ginger
1 teaspoon ground allspice
1/2 teaspoon ground nutmeg
1 cup canola or safflower oil
4 large eggs
1 cup granulated sugar
1 cup light brown sugar, packed
15 ounce can pumpkin puree
3/4 cup unsweetened apple sauce
1 tablespoon vanilla extract
1 cup shredded sweetened coconut (optional)
1 cup golden raisins (optional)
6 ounces chopped walnuts
1/2 cup confectioners' sugar
6 large egg yolks
3/4 cup sugar
1/2 cup light corn syrup
4 sticks unsalted butter, room temperature
1 tablespoon vanilla extract
1/8 teaspoon salt
Preheat oven to 350F°. Spray two 9-inch round cake pans with non-stick baking spray and set aside. In a large bowl, sift together flour, baking powder, baking soda, salt, cinnamon, ginger, allspice and nutmeg. In the bowl of an electric mixer fitted with the paddle attachment, beatt oil and eggs on medium speed until light, 3 minutes. Add both sugars; beat 2 minutes more. Beat in pumpkin, applesauce and vanilla. On low speed, add flour mixture, beating until just combined. Stir in coconut and raisins, if using.
Evenly distribute cake batter into the prepared pans and transfer to the oven. Bake until a toothpick inserted into the center comes out clean, 40 to 50 minutes. Let pans cool on a wire rack 15 minutes. Invert cakes onto rack; cool completely.
Make Toasted Walnut Paste: Preheat the oven to 350 F. Place the walnuts in a single layer on a baking sheet and toast them for 10 minutes, until fragrant. Cool 10 minutes. Place walnuts and confectioners' sugar in work bowl of a food processor fitted with a metal blade. Process until walnuts are very finely ground. Continue to process until the nut mixture until smooth and a "paste" texture forms.
Make the buttercream while the cake is baking: Beat the egg yolks in the clean bowl of an electric mixer fitted with the paddle attachment on medium-high until very thick, about 5 minutes. Combine the sugar with the syrup in a small saucepan, and set over medium-high heat, stirring constantly until the mixture comes to a full boil. Immediately scrape the mixture into a heatproof 1-cup glass measure. With the mixture on high speed, pour a few tablespoons of the sugar mixture into the yolks and beat for a few seconds. Repeat until all of the syrup has been added. Beat until the bowl has cooled to room temperature. On medium speed, beat in the butter, 2 tablespoons at a time, beating well after each addition. The frosting will begin to come together after all of the butter has been incorporated (it will look curdled first, but be patient and it will come together beautifully!). Scrape the bowl and beat in the vanilla and salt. Add the Pecan Paste and beat until well combined and smooth.
Cut each cake layer in half horizontally, creating four layers (trim any mounds off top of layers so that they are flat). Set one later, cut side up, on a cake round or cake plate and spread a layer of buttercream on the surface. Stack next layer on top and spread with a layer of buttercream. Repeat frosting-and-stacking process until each layer is frosted. Spread remaining frosting on sides and top of cake. Chill for 1 hour for easier slicing or serve immediately if you can’t wait!