When I need a crowd-pleasing dessert but don’t have all day, this lemon sheet cake is my go-to. I use a few simple pantry staples–like tangy sour cream and real lemon zest–to completely transform a standard vanilla cake mix. It’s bright, zesty, and so moist that nobody will believe it started with a box! Topped with a fluffy homemade lemon buttercream, this is one of my favorite desserts to serve in the summertime.
Lemon Sheet Cake with Buttercream Frosting
Lemon lovers, unite! I wanted to bring the best elements of my favorite lemon cupcakes to a delicious cake I could serve to a crowd. While I love the convenience of a box of vanilla cake mix, I find the texture can sometimes be a bit airy and one-note. To take my lemon sheet cake to a new level, I’ve replaced the standard oil and water with melted butter, buttermilk, and sour cream. The butter adds a rich, velvety flavor, while the buttermilk and sour cream provide the acidity needed to keep the cake incredibly tender and moist for days.
This recipe is my favorite because it bridges the gap between scratch-made and shortcut. By using just 7 simple ingredients, I can have a massive 13×18-inch sheet cake–enough to feed 24 people–prepped and in the oven in just 20 minutes. It’s my go-to for summer holidays when I want a high-impact dessert without the high-stress cleanup of multiple mixing bowls and equipment.
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Get More Juice from Your Lemons!
To get that signature zing, I don’t rely on artificial extracts. I use six real lemons between the cake and the frosting. By using both the freshly squeezed juice and the zest, you get a layered citrus flavor. The zest carries the aromatic oils that hit your nose first, while the juice provides that bright, tart finish that cuts through the sweetness of the powdered sugar.
To get the most juice possible, I recommend microwaving whole lemons for 10 seconds, then rolling them with firm pressure on a cutting board before juicing.
Lemon Sheet Cake Recipe
Equipment
- Kitchen Scale (optional)
- Baking Sheet (make sure it’s rimmed!)
- Hand Mixer
Ingredients
For the Cake:
- 26.5 ounces vanilla cake mix (2 (13.25-ounce) boxes)
- 1 cup unsalted butter melted (2 sticks)
- 4 large eggs room temperature
- ½ cup sour cream room temperature*
- ⅔ cup buttermilk room temperature**
- ⅓ cup freshly squeezed lemon juice (from about 3 lemons)**
- 2 tablespoons lemon zest (from 2 lemons)
For the Lemon Buttercream:
- 5 cups powdered sugar
- 1½ cups unsalted butter slightly melted (3 sticks)
- ⅓ cup freshly squeezed lemon juice (from about 3 lemons)
- 1 teaspoon lemon zest (from 1 lemon)
Instructions
- Preheat oven to 350°F. Line a 13×18-inch baking sheet with parchment paper (leave parchment paper slighter higher than the sides of the pan so it’s easier to lift the cake out after). Lightly spray parchment paper with nonstick spray then set aside.
- Mix the cake mix, butter, eggs, sour cream, buttermilk, lemon juice, and lemon zest in a large bowl.26.5 ounces vanilla cake mix, 1 cup unsalted butter, 4 large eggs, ½ cup sour cream, ⅔ cup buttermilk, ⅓ cup freshly squeezed lemon juice, 2 tablespoons lemon zest
- Pour the batter onto the prepared sheet cake pan and use a spatula to evenly distribute the cake batter in the pan.
- Bake in the preheated oven for 27-28 minutes, or until a toothpick inserted in the middle comes out clean.
- Remove cake from oven and let cool completely before frosting.
- While the cake cools, make the frosting: In a large bowl, beat the powdered sugar, butter, lemon juice, and lemon zest on low speed until well combined then beat on high until frosting is light and fluffy, about 5 minutes. If the frosting seems too thick, beat in an additional tablespoon of lemon juice.5 cups powdered sugar, 1½ cups unsalted butter, ⅓ cup freshly squeezed lemon juice, 1 teaspoon lemon zest
- Smooth an even layer of frosting over the top of the cake and decorate as desired.
Notes
- For a stronger lemon flavor, rub the lemon zest and dry cake mix together between your fingers to release more of the citrus oils into the batter.
- The lemon juice could cause the batter to look a bit curdled when combined with the buttermilk and sour cream, but this won’t affect how the cake turns out.
- The flavor compounds found naturally in lemons are susceptible to heat, meaning they can burn off in the oven. I added tons of juice and zest, but if you’re nervous about the flavor, you can also add a teaspoon of lemon extract.
- Resist the urge to add extra lemon juice to the batter; the excess moisture will cause the cake to collapse in the oven!
- Once the batter is spread, bang the pan firmly on the counter 3-4 times. This pops large air bubbles that can cause the cake to sink in the center.
- The butter should dent when pressed but not be shiny. If it’s too warm, your frosting will turn out soupy.
- If the frosting feels too soft after mixing, pop the whole bowl in the fridge for 15 minutes before spreading.
- If you find the frosting is pulling up bits of cake, put a very thin layer of frosting on first (the crumb coat), freeze the cake for 10 minutes, then apply the rest of the fluffy buttercream.
How to Make Lemon Sheet Cake with Boxed Mix Step-by-Step
Mix the Batter: Preheat your oven to 350°F, line a 13×18-inch baking sheet with parchment paper and lightly spray with nonstick spray, and set aside. Mix 26.5 ounces (2 boxes) of vanilla cake mix, 1 cup of melted unsalted butter, 4 large eggs, ½ cup of sour cream, ⅔ cup of buttermilk, ⅓ cup of freshly squeezed lemon juice, and 2 tablespoons of lemon zest in a large bowl. For a stronger lemon flavor, rub the lemon zest and dry cake mix together before adding the other ingredients to release citrus oil. Don’t panic if the batter looks curdled; it’s a natural reaction from the lemon juice and totally harmless.
Smooth the Batter: Pour the batter onto the prepared sheet cake pan and use a spatula to evenly distribute the cake batter in the pan. Lift the pan up and bang it on your countertop 3-4 times to pop any air bubbles for a more even bake.
Bake the Cake: Bake your lemon sheet cake in the preheated oven for 27-28 minutes, or until a toothpick inserted in the middle comes out clean. Remove the cake from the oven and let it cool completely before frosting.
Make the Frosting: In a large bowl, beat 5 cups of powdered sugar, 1½ cups of slightly melted unsalted butter, ⅓ cup of freshly squeezed lemon juice, and 1 teaspoon of lemon zest on low speed until well combined. Beat on high until frosting is light and fluffy, about 5 minutes. If the frosting seems too thick, beat in an additional tablespoon of lemon juice.
Frost the Cake: Smooth an even layer of frosting over the top of the sheet cake and decorate as desired. If the frosting is pulling up bits of dry cake, try crumb-coating the cake in a thin layer of frosting first, chill for 10 minutes, then finish frosting for a smoother finish. I love adding fresh berries and lemon slices for a beautiful, summer-y finish!
How to Store and Freeze
Store frosted lemon sheet cake in an airtight container at room temperature for up to 3 days, in the refrigerator for up to 5 days, or in the freezer for up to 3 months. Let thaw overnight in the refrigerator before enjoying chilled or at room temperature.
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