King Arthur's Favorite Fudge Cake

Recipe by PJ Hamel

This old-fashioned chocolate sheet cake is incredibly moist, and can be stirred together by hand if need be. The fudge frosting is also stir-together simple, and creates a lovely thick layer on top. You can line the pan with parchment or foil before baking, grease it, and lift the cake out of the pan once it's cool before frosting. This makes cutting the cake easier to do, and individual portions nestle nicely into muffin papers. It's sure to be a hit at your next potluck.

Want to make two dozen cupcakes instead of a layer cake? See "tips," below.

20 mins
30 mins
1 hr 20 mins
one 9" x 13" cake
King Arthur's Favorite Fudge Cake - select to zoom
King Arthur's Favorite Fudge Cake - select to zoom
King Arthur Flour's Favorite Fudge Cake - select to zoom


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  1. Preheat the oven to 350°F. Grease and flour a 9" x 13" pan.

  2. To make the cake: Melt the butter; stir in the cocoa and hot water. In a separate bowl, combine the flour, sugar, soda, and salt.

  3. Pour the cocoa mixture over the dry ingredients, stirring to blend. Beat in the buttermilk or yogurt, eggs, and vanilla. Pour the batter into the prepared pan.

  4. Bake the cake for 30 minutes, or until it tests done. You'll smell the chocolate aroma, and the cake will begin to pull away from the edge of the pan. Remove the cake from the oven and cool it on a rack.

  5. To make the frosting: Melt the butter in a medium-sized saucepan. Stir in the cocoa and buttermilk or yogurt.

  6. Bring the mixture to a boil, then remove it from the heat and mix in the confectioners' sugar, beating until smooth.

  7. Pour the frosting over the cake while the frosting is still warm. Serve the cake right from the pan.

Tips from our Bakers

  • This makes a typical sheet cake, which means it's fairly flat: about 1" to 1 1/4" tall. For a more substantial cake, one that's about 1 1/2" to 2" tall, increase all of the cake ingredients by 50%, and bake the cake for 40 to 45 minutes, until it tests done. The frosting measurements will remain the same.
  • To bake as cupcakes: Line two muffin pans with cupcake papers and grease the papers. Preheat the oven to 350°F. Prepare the batter as directed above, then portion into the prepared pan, filling each well about 2/3 full. 

    Bake the cupcakes for 21 to 23 minutes, until a paring knife inserted in the center of a cupcake comes out clean. Remove from the oven and cool in the pan for 5 minutes before tipping the cupcakes out of the pan to cool on a rack.

    To frost, make the frosting as directed and dip the cupcakes in the frosting while it’s still warm, letting the excess drip back into the pan. Sprinkle the tops with decorations before the frosting sets (this will happen quickly). If the frosting starts to set before you’ve dipped all the cupcakes, add a tablespoon of water and reheat gently, whisking until smooth.