Texas Sheet Cake

Before you start

Texas sheet cake is built for potlucks: a large, thin chocolate cake baked in a rimmed half-sheet pan, then covered while still warm with a poured cocoa icing studded with pecans. Butter, water and cocoa are boiled together for the batter, and buttermilk keeps the crumb tender and slightly tangy. The whole thing is mixed in a saucepan and a bowl, with no mixer needed.

Timing is the only real trick. Start the icing in the last few minutes of baking and pour it over the hot cake straight away. Warm icing on warm cake melts slightly into the top and then sets into a thin, crackly, fudgy layer. If the cake cools first, the icing sits on top like ordinary frosting.

Ingredients

• Cake250 g (2 cups, spooned and leveled) all-purpose flour
• 400 g (2 cups) granulated sugar
• 1 tsp baking soda
• ½ tsp fine salt
• ½ tsp ground cinnamon — optional
• 225 g (1 cup) unsalted butter
• 240 ml (1 cup) water
• 25 g (¼ cup) unsweetened natural cocoa powder
• 120 ml (½ cup) buttermilk
• 2 large eggs
• 1 tsp vanilla extract
• Icing115 g (½ cup) unsalted butter
• 25 g (¼ cup) unsweetened natural cocoa powder
• 90 ml (6 tbsp) whole milk
• 450 g (about 3¾ cups) powdered sugar — sifted
• 1 tsp vanilla extract
• 115 g (1 cup) pecans — toasted and chopped

Method

1. Heat the oven to 175°C (350°F). Grease the half-sheet pan well, or line it with parchment.
2. Whisk the flour, sugar, baking soda, salt and cinnamon in a large bowl.
3. Bring the butter, water and cocoa to a boil in a saucepan, whisking until smooth. Pour the hot mixture over the dry ingredients and whisk until just combined.
4. Whisk the buttermilk, eggs and vanilla in a small bowl, then whisk them into the batter until smooth. It will be thin and pourable.
5. Pour into the pan and tilt to spread it evenly into the corners. Bake for 18 to 22 minutes, until the cake springs back when pressed and a toothpick comes out clean.
6. About 5 minutes before the cake is done, melt the icing butter with the cocoa and milk in the second saucepan, bringing it just to a simmer. Off the heat, whisk in the powdered sugar and vanilla until smooth, then stir in the pecans.
7. As soon as the cake comes out, pour the warm icing over it and spread it quickly to the edges with an offset spatula. It will settle into a smooth, even layer.
8. Cool the cake in the pan on a rack for about 1 hour, until the icing has set to a soft, glossy crust. Cut into 24 squares.

Tips for success

• Use natural cocoa, not Dutch-process. The cake relies on baking soda reacting with the acid in natural cocoa and buttermilk for its lift.
• Have every icing ingredient measured before the cake goes in the oven. The icing comes together fast and needs to meet a hot cake.
• Rotate the pan halfway through baking if your oven has hot spots; a thin cake shows uneven heat quickly.

Substitutions

Buttermilk

Stir 1½ tsp lemon juice into 120 ml milk and wait 5 minutes, or use 120 g plain yogurt thinned with a little milk.

Half-sheet pan

A 25 x 38 cm (10 x 15 in) jelly-roll pan makes a thicker cake; bake 22 to 26 minutes. A 23 x 33 cm (9 x 13 in) pan needs 30 to 35 minutes and gives a conventional cake.

Pecans

Walnuts work the same way, or leave nuts out entirely for a smooth icing.

Variations

Espresso sheet cake

Replace the water in the cake with hot brewed coffee and add 1 tsp instant espresso to the icing.

White Texas sheet cake

Leave out the cocoa, use 1 tsp almond extract in the cake and icing, and top with sliced almonds.

Troubleshooting

Icing is grainy

The powdered sugar had lumps or the mixture got too hot. Sift the sugar and take the pan off the heat before adding it.

Icing set before it spread

It sat too long or the cake had cooled. Make the icing at the end of baking and pour it immediately, warming it gently if it thickens.

Cake is dry around the edges

It overbaked; thin cakes go from done to dry in a few minutes. Start checking at 17 minutes.

Storage

Cover the pan and keep the cake at room temperature for up to 3 days. Squares freeze well, wrapped individually, for up to 2 months.

Safety notes

Do not taste the raw batter, which contains raw flour and eggs. Contains wheat, egg, milk and tree nuts (pecans).