Equipment
* optional
Ingredients
Cake Batter
- 260 g all-purpose flour, dry
- 350 g granulated sugar, dry
- 35 g unsweetened natural cocoa powder, sifted
- 5 g baking soda, dry
- 4 g fine salt, dry
- 115 g unsalted butter, solid
- 60 ml vegetable oil, liquid
- 240 ml water, liquid
- 120 ml buttermilk, room temperature
- 2 egg, room temperature
- 10 ml vanilla extract, liquid
Mild Chocolate Glaze
- 85 g unsalted butter, solid
- 60 ml whole milk, liquid
- 20 g unsweetened natural cocoa powder, sifted
- 250 g powdered sugar, sifted
- 5 ml vanilla extract, liquid
Nutrition (per serving)
Nutrition is estimated per serving. Nutrients without complete source data are omitted.
Full nutrition
- Calories
- 350 kcal
- Protein
- 4 g
- Carbohydrates
- 53 g
- Fat
- 15 g
- Fiber
- 2 g
- Sugar
- 38 g
- Sodium
- 208 mg
- Saturated Fat
- 7 g
- Monounsaturated Fat
- 4 g
- Polyunsaturated Fat
- 3 g
- Cholesterol
- 51 mg
- Potassium
- 100 mg
- Calcium
- 28 mg
- Iron
- 1.4 mg
- Magnesium
- 23 mg
- Phosphorus
- 68 mg
- Zinc
- 0.5 mg
- Vitamin A
- 98 mcg
- Vitamin C
- 0 mg
- Vitamin E
- 0.7 mg
- Vitamin K
- 7 mcg
- Vitamin B6
- 0.0 mg
- Vitamin B12
- 0.1 mcg
- Thiamin
- 0.14 mg
- Riboflavin
- 0.15 mg
- Niacin
- 1.1 mg
- Folate
- 35 mcg
- Water
- 35 g
- Alcohol
- 0 g
- Caffeine
- 8 mg
Sources: USDA FoodData Central
Method
Preheat the oven to 175°C (350°F), grease the 23x33 cm (9x13 inch) metal baking pan with butter, and line the bottom with parchment paper.
Sift the all-purpose flour, granulated sugar, 35 grams of unsweetened natural cocoa powder, baking soda, and fine salt through the fine-mesh sieve into the large mixing bowl.
Whisk the sifted dry ingredients together in the large mixing bowl until completely combined.
Combine 115 grams of unsalted butter, the vegetable oil, and water in the medium saucepan over medium heat until the butter melts and the liquid reaches a gentle boil.
Pour the hot butter and water mixture into the dry ingredients in the large mixing bowl and whisk until smooth and hydrated.
Whisk the buttermilk, room temperature eggs, and 10 milliliters of vanilla extract into the batter in the large mixing bowl until fully incorporated.
Pour the batter into the prepared 23x33 cm (9x13 inch) metal baking pan and gently level the surface with the silicone spatula.
Bake in the preheated oven at 175°C (350°F) for 20 minutes until a toothpick inserted in the center comes out clean or with a few moist crumbs and an instant-read digital thermometer registers at least 95°C (203°F).
Cool the cake in its pan on the wire cooling rack for 15 minutes before making the glaze.
Melt 85 grams of unsalted butter with the whole milk and 20 grams of cocoa powder in the medium saucepan over medium-low heat while whisking constantly until smooth.
Whisk the sifted powdered sugar and 5 milliliters of vanilla extract into the warm chocolate butter mixture in the medium saucepan off the heat until glossy and lump-free.
Pour the warm glaze immediately over the warm cake in the pan, spreading it evenly to the edges with the silicone spatula.
Rest the glazed cake in the pan on the wire cooling rack for 25 minutes at room temperature until the frosting sets into a tender skin before slicing into 16 squares.
Chef's Notes
- Using natural cocoa powder instead of Dutch-process keeps the chocolate flavor gentle, milk-chocolate-like, and approachable without intense bitter undertones.
- Pouring warm icing directly onto a warm sheet cake allows a subtle micro-layer of frosting to penetrate the top crumb, producing an exceptionally moist barrier.
- The split fat approach—combining rich dairy butter with neutral vegetable oil—delivers comforting butter flavor alongside the lasting softness that only liquid oils provide at room temperature.
- Buttermilk provides mild lactic acidity that tenderizes wheat gluten and reacts with baking soda to produce a fine, tender crumb without lingering chemical taste.
Storage
Refrigerator: 5 days — Store in an airtight container or cover the baking pan tightly with foil or plastic wrap. Bring slices to room temperature for 20 minutes before serving to restore crumb softness.
Freezer: 2 months — Wrap individual sliced squares tightly in plastic wrap and store inside an airtight freezer-safe container. Thaw wrapped slices in the refrigerator overnight.
Reheating: Reheat a refrigerated slice on a microwave-safe plate on 50 percent power for 10 to 15 seconds to gently soften the crumb and glaze without melting the icing into a liquid.
Troubleshooting
Cake crumb is dense or dry rather than light and plush
Cause: Flour was packed into a measuring cup or cake was overbaked past 98°C (208°F)
Fix: Cannot be fixed once fully baked; brush warm simple syrup or warm milk lightly over the cake surface before glazing to rehydrate the crumb
Prevention: Weigh flour precisely with a kitchen scale and test for doneness starting at 18 minutes
Chocolate glaze separates into greasy pools or turns grainy
Cause: Glaze was heated too high, causing the butter fat to break, or powdered sugar was not sifted
Fix: Whisk in 10 to 15 milliliters of hot whole milk vigorously off the heat until the emulsion re-forms smoothly
Prevention: Remove the saucepan from the heat before adding sifted powdered sugar and keep heat low while melting butter
Cultural Context
The chocolate sheet cake gained legendary status in mid-twentieth-century American community cookbooks and church potlucks, particularly across Texas and the South. Its trademark boiled-liquid method simplifies production while ensuring a reliably tender crumb, crowned with a warm cooked glaze that sets directly in the baking pan.
