My Mom’s Chocolate Sheet Cake
Once you taste my mom’s Chocolate Sheet Cake you’ll be hooked. This ultra moist and tender dessert has a beautiful glossy poured frosting. beauties topped with glossy poured frosting, you’ll understand why they are so popular. These are sometimes called Buttermilk Brownies or Cake Brownies but regardless of what you call them, you are in for a treat!
Why You’ll Love This Chocolate Sheet Cake
- Perfect texture: Light, cakey, and incredibly tender—not dense or fudgy—thanks to buttermilk, baking soda, and a smart butter-avocado oil blend that keeps every bite moist for days.
- Balanced chocolate flavor: Mild and approachable, with cocoa bloomed on the stove for depth and a subtle hint of espresso powder that makes the chocolate sing without overpowering.
- That iconic frosting: The poured, boiled frosting sets into a glossy, fudgy layer with a signature crackly top—everyone fights over the pieces with the most of it.
- Crowd-pleaser: Feeds a big group (24–30 squares), easy to transport, and tastes even better the next day—ideal for potlucks, parties, or family gatherings.
- Nostalgic and forgiving: Simple ingredients, straightforward steps, and reliable results that capture the comforting taste of home without complicated techniques.
My History With This Decadent Dessert
For several years, my mom worked for a caterer and she shamelessly pilfered this recipe (that I’ve made a few adjustments and scaled down to a jelly roll pan size). Since then she has baked this chocolate sheet cake for potlucks, family reunions, birthdays, or simply because the pantry had cocoa and buttermilk. She always called them “brownies,” even though they’re far more tender and cake-like than any fudgy brownie. They are incredibly simple but pack a big punch! It’s still unmistakably hers—just a little more reliable for home bakers.
Tips for Making Chocolate Sheet Cake
- Sift the flour through a fine-mesh sieve to prevent clumps—essential with this thin batter.
- Bloom the cocoa properly: heat gently until steaming (no boiling) to unlock maximum chocolate flavor without bitterness.
- Work quickly with the frosting—pour and spread within 1–2 minutes while it’s hot and fluid for that glossy, crackly finish. If it thickens mid-spread, gently re-warm over low heat for 10–15 seconds and limit spreading with a spatula. See my photo below where I got a little too aggressive with spreading the rapidly cooling frosting.
- Don’t overmix the batter after adding wet to dry—gentle whisking keeps the crumb tender.
- Cool completely before frosting so the hot icing doesn’t melt into the cake unevenly.
- Pan fit—this scaled version leaves about ½ inch clearance before baking; if your pan is slightly smaller, reduce water to 1 cup next time.
- Storage—keep covered at room temperature up to 3 days; the avocado oil helps maintain moisture beautifully. This cake freezes beautifully as well. Just cut and freeze in a single layer in an airtight container and separate with wax paper or plastic wrap if layering.
Final Thoughts
This chocolate sheet cake isn’t fancy or complicated—it’s honest, comforting, and exactly the kind of dessert that brings people together. Bake it for your next gathering, cut big squares, and watch the corners vanish first. Then save a piece for yourself; you’ve earned it. Mom would approve.
Happy baking!
Chocolate Sheet Cake
Print RecipeTender buttermilk chocolate sheet cake with a glossy poured frosting. Moist, cakey, and mildly chocolatey—perfect for potlucks and family gatherings. Nostalgic and crowd-pleasing!
Servings: 30 squares
EQUIPMENT (affiliate links)
Ingredients
Cake Ingredients
- 2½ c. (310 g) unbleached all-purpose flour (RECOMMEND WEIGHING)
- 2½ c. (500 g) granulated sugar
- ½ tsp. salt
- ½ c. (113 g) salted butter
- ½ c. (110 g) avocado oil (or neutral oil)
- 1¼ c. (300 g) water
- ¼ c. (25 g) unsweetened cocoa powder
- ½ tsp. espresso powder optional
- 3 large eggs
- ⅔ c. (160 g) buttermilk
- 1¼ tsp baking soda
Frosting Ingredients
- ⅓ c. (80 g) milk
- 1½ c. (300 g) granulated sugar
- 5 tbsp. (70 g) salted butter, softened
- ¾ c. (130 g) semisweet chocolate chips
Instructions
- Preheat oven to 325°F (165°C). Grease a 15×10-inch jelly roll pan thoroughly (butter or nonstick spray). Optional: line the bottom with parchment.
- Sift the flour through a fine-mesh sieve into a large bowl. Add the sugar and salt. Whisk 20–30 seconds to aerate and combine. Set aside.2½ c. (500 g) granulated sugar2½ c. (310 g) unbleached all-purpose flour (RECOMMEND WEIGHING)½ tsp. salt
- In a medium saucepan over medium-low heat, melt the butter. Add the avocado oil, water, cocoa powder, and espresso powder (if using). Stir constantly until smooth and just steaming (2–3 minutes; do not boil). Remove from heat and cool slightly.½ c. (113 g) salted butter½ c. (110 g) avocado oil (or neutral oil)1¼ c. (300 g) water¼ c. (25 g) unsweetened cocoa powder½ tsp. espresso powder
- In a separate bowl, whisk the 3 eggs, ⅔ cup buttermilk, and 1¼ teaspoons baking soda until smooth. To temper (recommended for extra safety): Add a small ladle (~¼ cup) of the warm cocoa mixture to the egg blend while whisking constantly. Repeat 2–3 times until the egg mixture feels warm. Then slowly pour in the remaining cocoa mixture while whisking vigorously.3 large eggs⅔ c. (160 g) buttermilk1¼ tsp baking soda
- Pour the wet mixture into the dry ingredients and whisk until smooth and no dry pockets remain. The batter will be thin and pourable. Pour into the prepared pan and spread evenly (should leave about ½ inch clearance from the top edge).
- Bake 30–36 minutes (check at 30 minutes). A toothpick inserted in the center should come out clean or with moist crumbs. Cool completely in the pan (~1 hour).
- In a medium saucepan, combine milk, sugar, and butter. Bring to a boil over medium heat, stirring constantly. Boil exactly 60 seconds, then remove from heat. Stir in chocolate chips until fully melted and smooth.⅓ c. (80 g) milk1½ c. (300 g) granulated sugar5 tbsp. (70 g) salted butter, softened¾ c. (130 g) semisweet chocolate chips
- Immediately pour the warm frosting over the cooled cake. Spread quickly and evenly with an offset spatula or knife for a glossy finish (work within 1–2 minutes before it sets).
- Let frosting set (~30 minutes), then cut into squares. Store airtight at room temperature for up to 2–3 days or freeze for 3 to 4 months.
Notes
- Avocado oil helps maintain moisture for days while the butter adds richness.
- Sift flour to prevent clumps.
- Bloom cocoa gently for best flavor.
- If frosting thickens while spreading, gently rewarm over low heat for 10–15 seconds.
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