Classic Yellow Cake with Chocolate Frosting

For the cake:
4 1/4 cups cake flour
1 Tbsp plus 1 tsp baking powder
1 tsp salt
2 1/4 cups milk
1 1/2 Tbsp vanilla extract
20 Tbsp (2 1/2 sticks) unsalted butter, at room temperature
2 1/2 cups granulated sugar
5 eggs

For the frosting:
8 ounce unsweetened chocolate, finely chopped
1 1/3 cups unsalted butter, at room temperature
3 cups confectioners' sugar, sifted

Have all the ingredients at room temperature. Preheat an oven to 350°. Grease and flour a 9x13 inch cake pan

To make the cake, over a sheet of waxed paper, sift together the flour, baking powder and salt; set aside.

In a small bowl, combine the milk and vanilla; set aside.

In the bowl of an electric mixer fitted with the flat beater, beat the butter on medium speed until smooth, about 2 minutes. Add the granulated sugar and beat until light and fluffy, about 5 minutes. Add the eggs, one at a time, beating well after each addition. Reduce the speed to low and add the flou mixture in four additions, alternating with the milk mixture and beginning and ending with the flour. Beat each addition until just incorporated, stopping the mixer occasionally to scrape down the sides of the bowl.

Spoon the batter into the prepared pan and spread the batter evenly. Bake until the cake begins to pull away from the sides of the pan and a toothpick inserted into the center comes out clean, 35 to 40 minutes. Transfer the pan to a wire rack and let the cake cool completely in the pan.

To make the frosting, in a heatproof bowl set over but not touching simmering water in a saucepan, melt the chocolate; let cool to room temperature. In the bowl of an electric mixer fitted with flat beater, beat the butter on medium speed until smooth, about 30 seconds. Add the confectioners' sugar and beat until smooth, creamy and slightly fluffy, about 3 minutes. Beat in the melted chocolate, scraping the sides and bottom of the bowl to evenly distribute chocolate.

Using and icing spatula or a knife, spread the frosting over the top of the cake, reserving some for piping, if desired. Refrigerate the cake for 30 minutes before serving to set the frosting.

Williams Sonoma recipe