Moist & Fudgy Gluten-Free Texas Sheet Cake
yields: 24 slices
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 oat, millet, and sweet rice flours create a moist, tender crumb. Baked in just 24 minutes in a half-sheet pan — no cooling before frosting. It’s perfect for a crowd, with optional pecans for toasty crunch!
Equipment
Ingredients
Chocolate Cake
- 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
Fudgy Icing
- 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
Optional
- 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.