This gluten-free Texas sheet cake is rich and deeply chocolatey with warm, fudgy icing poured right over the hot cake. Buttermilk and plenty of butter keep it nostalgic, while the perfect blend of gluten-free flours creates the most tender crumb. Baked for just 24 minutes in a half-sheet pan, it's the perfect cake for feeding a crowd. Optional pecans folded into the icing add a toasty crunch!
I'd normally slap your wrist if you tried frosting a hot cake, but this gluten-free Texas sheet cake is the exception. It requires you to pour the warm fudgy icing over the hot-out-of-the-oven chocolate cake. As it cools, the icing seeps into the crumb and melds with the cake, instead of just sitting on top.
The result: a thin, deeply rich and moist gluten-free chocolate cake crowned with a thick, gooey, fudgy icing that's every bit the main event as the cake beneath it.
While nuts are optional, you can take this comforting cake over the edge by folding toasted pecans into the icing. Their nutty crunch becomes part of that bold, fudgy layer instead of just perching on top.
With only a 24-minute bake in a half-sheet pan and no cooling before frosting required, this sheet cake saves you when you want to impress a crowd, but are short on time. The fastest gluten-free chocolate sheet cake in the West.
Frost it while it's Hot
The boiled chocolate frosting gets poured on while the cake is still hot. You'll let the cake sit for 3 minutes after coming out the oven (this is the one small difference with a gluten-free version), giving the crumb a few minutes to firm up so it doesn't sink under the weight of the icing.
I know gluten-free chocolate cake.
My gluten-free chocolate cake is the gold standard. Deeply chocolatey. Ultra-moist. I've made it more than 300 times over the past decade - as a classic gluten-free chocolate sheet cake, a gluten-free triple chocolate layer cake, and the most tender gluten-free chocolate cupcakes. It's the cake that sparks bidding wars at the school auction. The cake that defines me.
After hundreds of tests and nearly a decade of trust, that's where I started, using the same oat, sweet rice, and millet flour blend as my signature chocolate cake. The result? A plush, melt-in-your-mouth chocolate cake that's never fragile, grainy, gummy, or dense - just perfect every time.
- Gluten-free oat flour adds lift, keeping it tender and moist.
- Sweet rice flour adds chew. Also called mochiko, it's the very same flour used to make mochi cake. As such, it's the chewy glue that holds the cake together like a classic gluten-filled cake.
- Millet flour is a light neutral flour that prevents the cake from becoming gummy and dense.
The Nitty Gritty of Old-Fashioned Texas Sheet Cake
The two variables that change from one Texas sheet cake recipe to the next are the type of liquid and the amount of butter called for. After lots of testing, this is what makes the best chocolate slab cake:
- Buttermilk: I tested this with buttermilk vs. milk + vinegar, and buttermilk won by a landslide. Its acidity activates the baking soda for better lift and a more tender crumb - especially important in a thin cake like this. Milk works in a pinch, but buttermilk gives the best texture and adds a subtle tang to the icing, too.
- Butter: Non-negotiable. In a thin cake, butter delivers the richness that keeps it moist and plush, not dry. It also blooms the cocoa for deeper chocolate flavor, and gives the fudge-like icing its signature soft-set texture.
Why I Add Baking Soda to the Buttermilk, not Dry Ingredients
Stirring the baking soda into the acidic buttermilk jumpstarts the reaction before it hits the batter, giving this thin cake the lift it needs. When I tested whisking it into the dry ingredients instead, the cake baked up noticeably flatter. In a cake this thin, every bit of lift counts.
Recipe
Moist & Fudgy Gluten-Free Texas Sheet Cake
Equipment
Ingredients
- 1 cup (227 g) unsalted butter, 2 sticks, plus 1 tablespoon for greasing the pan
- 1 cup (240 g) hot water
- 34 g (5 tablespoons) unsweetened dutch-processed cocoa powder, or sub natural cocoa powder
- 110 g (½ cup + 3 tablespoons) sweet rice flour, also called mochiko; do not substitute white or brown rice flour
- 81 g (¾ cup) gluten-free oat flour
- 74 g (½ cup) millet flour
- 400 g (2 cups) granulated sugar
- ½ teaspoon kosher salt
- ½ cup (120 g) buttermilk, see note
- 2 large eggs, room temperature
- 1 teaspoon baking soda
- 1 teaspoon pure vanilla extract
- 4¾ cups (570 g) powdered sugar
- 12 tablespoons (6 oz) unsalted butter, 1½ sticks
- ½ cup + 1 tablespooon (135 g) buttermilk, or sub whole milk
- 6 tablespoons (41 g) unsweetened dutch-processed cocoa powder, or sub natural cocoa powder
- 1½ teaspoons pure vanilla extract
- ¼ teaspoon kosher salt
- 1 cup (4 oz) toasted pecan pieces
INSTRUCTIONS
- Preheat oven to 350°F and grease an 18x13 half sheet baking pan with butter. Set aside.
- In a large mixing bowl, sift together oat flour, sweet rice flour, millet flour, sugar, and salt. Set aside.
- Melt butter in a medium saucepan over medium heat. Once melted, whisk in cocoa powder, followed by hot water until smooth. Bring to a boil and cook for 30 seconds longer, stirring constantly. Pour this chocolate butter mixture over the dry ingredients and whisk to combine. Set aside.
- In a measuring cup, whisk together the buttermilk and eggs until well combined. Whisk in the baking soda and vanilla. Pour buttermilk egg mixture into the chocolate batter and whisk until completely smooth.
- Pour batter into the prepared pan, spreading into an even layer. Bake for 24 minutes, until the cake springs back in the center when gently touched.
- Meanwhile, prepare the icing with about 10 minutes left on the clock. Sift the powdered sugar into a medium mixing bowl and set aside.
- Wash and return the same saucepan to the stove. Bring butter, buttermilk, and cocoa powder to a boil over medium heat, whisking until smooth.
- Pour boiling chocolate butter mixture over the powdered sugar, followed by vanilla and salt. Whisk until completely smooth. If using, fold in toasted pecan pieces.
- When the cake comes out of the oven, let it sit for 3 minutes so the gluten-free crumb can just set enough that it doesn't collapse under the weight of the icing. Give the icing a quick stir to make sure it's smooth, then pour it over the hot cake, gently spreading it into an even layer with an offset spatula. Let cool for at least 15 minutes before slicing. Store leftovers, covered, at room temperature for up to 3 days, or freeze for longer storage.
Video
Notes
Buttermilk Substitute
You can replace the buttermilk with ½ tablespoon vinegar mixed with scant ½ cup whole milk in the cake, and replace the buttermilk in the icing with whole milk. Note that your cake will be slightly thinner and less rich with milk.Small Batch
Don't need a giant sheet cake? Halve the recipe and bake it in a quarter-sheet pan (9 x 13). Reduce the baking time by 1-2 minutes, checking for doneness around 21 minutes.Did you make this recipe? Please leave a review and rating to let me and others know how you liked it!
How to Make the Fastest Frosted Gluten-Free Chocolate Cake
Sift together flours, sugar, and salt and set aside.
Melt butter in a medium saucepan over medium heat.
Whisk in the cocoa powder and hot water until smooth.
Bring to a boil and cook for 30 seconds longer, stirring constantly.
Pour chocolatey butter over the dry ingredients...
...and whisk until completely smooth.
In the measuring cup, whisk the eggs into the buttermilk with a fork until well combined.
Then whisk in the baking soda and vanilla.
Pour egg-buttermilk mixture into cake batter...
...and whisk until completely smooth with no lumps remaining.
Pour chocolate cake batter into an 18x13 baking sheet, greased well with butter.
Spread into a thin, even layer and bake at 350°F for 24 minutes.
That Glossy Fudge Layer
While it bakes, make the fudgy chocolate icing. You'll spread it over the hot cake, so no need to wait.
Wash and use that same pan. Add butter, buttermilk, and cocoa powder and cook over medium heat, stirring until the butter melts.
Whisk until smooth and bring to a boil.
Pour chocolatey butter mixture over sifted powdered sugar...
...and stir until completely smooth and glossy.
If using, add toasted pecan pieces...
...and stir until well combined.
Pull the cake from the oven and let it sit just 3 minutes to allow the gluten-free crumb to set. Then give the icing a quick stir to make sure it's smooth without a skin on top, then pour it over the hot cake.
Spread icing into an even layer with an offset spatula.
Let sit for about 15 minutes for the icing to set before slicing and serving.
Hint: Wipe any frosting and nuts off the knife with a paper towel between cuts to make cleaner slices.
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