Active Time

　　50 minutes

　　Total Time

　　1 hour, 50 minutes

　　Real milk chocolate—not just cocoa powder—gives this cake its rich, chocolatey flavor. With a foolproof, one-bowl preparation, effortless frosting, and portability, this cake is sure to be your new go-to for special occasions and backyard barbecues.

　　

Ingredients

Serves 15

　　

For the cake:

1 cup (2 sticks) unsalted butter, plus more for pan

　　1/2 cup plus 2 tablespoons unsweetened cocoa powder, divided

　　6 ounces high-quality milk chocolate, chopped

　　3 large eggs

　　2 teaspoons vanilla extract

　　1 3/4 cups sugar

　　1 1/4 cups buttermilk

　　2 cups all-purpose flour

　　1 1/2 teaspoons baking powder

　　1/2 teaspoon baking soda

　　1/2 teaspoon kosher salt

　　

For the frosting:

9 ounces high-quality milk chocolate, divided

　　1 teaspoon vanilla extract

　　1/4 teaspoon kosher salt

　　3/4 cup heavy cream

　　1/2 cup store-bought dulce de leche or caramel sauce

　　

Bake the cake:

Step 1

Preheat oven to 350°F. Butter a 13x9" pan and dust with 2 Tbsp. cocoa powder, tapping out excess.

　　

Step 2

Melt remaining 1 cup butter in a small saucepan over medium heat. Add chocolate and remaining 1/2 cup cocoa powder; cook, whisking constantly, until smooth. Let cool slightly.

　　

Step 3

Whisk eggs and vanilla in a large bowl. Add sugar and whisk until smooth, lightened in color, and slightly aerated, about 2 minutes. Stream in buttermilk while whisking, then stream in chocolate mixture while whisking until smooth.

　　

Step 4

Sift flour, baking powder, baking soda, and salt into chocolate mixture. Whisk until batter is mostly smooth (there will be a few small lumps). Transfer to prepared pan.

　　

Step 5

Bake cake until a tester inserted into the center comes out clean, 35–40 minutes. Transfer pan to a wire rack and let cake cool completely.

　　

Make the frosting:

Step 6

Slice 2 oz. chocolate into long, thin shards; reserve for decorating. Coarsely chop remaining 7 oz. chocolate and transfer to a medium bowl. Add vanilla and salt.

　　

Step 7

Heat cream in a small pot over medium until just starting to simmer. Pour over chocolate mixture and let sit 3 minutes. Whisk until chocolate is melted and smooth. Whisk in dulce de leche. Chill until firm, at least 1 hour.

　　

Step 8

Whisk frosting to lighten and loosen, then use a spatula to spread over cake. If it's too stiff to work with, let it sit out on the counter for a few minutes. Sprinkle with reserved chocolate shards. Cut into thirds lengthwise, then into fifths crosswise (you should have 15 pieces).

　　

Do Ahead

Step 9

Cake can be made 3 days ahead; cover and chill. Bring to room temperature before serving.