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This blueberry sheet Cake is one of those recipes you’ll make once and never stop making. It’s bright with Lemon, packed with fresh blueberries, and topped with a blueberry cream cheese frosting that’s such a gorgeous shade of purple it’ll stop everyone in their tracks. Simple to pull together, feeds a crowd, and so much more impressive than it has any right to be for a 9×13 pan.
Why You’ll Love This Cake
- That frosting. Blueberry cream cheese whipped until it’s light, airy, and a stunning shade of purple — it’s reason enough on its own.
- Real blueberry flavor in every bite. Fresh blueberries throughout the cake, not just a few on top.
- Bright lemon flavor from three full lemons’ worth of zest — it makes the whole thing sing.
- Incredibly tender crumb thanks to Buttermilk in the batter. It stays moist for days.
- No fussy layers or stacking. A 9×13 pan, one batch of frosting, and you’re done.
A Few Notes on the Ingredients
The lemon situation in this cake is no joke. We’re talking three lemons’ worth of zest, minimum. I know that sounds like a lot but trust it — that’s where the brightness comes from and you’ll notice immediately if you try to cut corners. I have tried to cut corners. I was in a hurry once and only used two lemons and the cake was fine but it wasn’t the same. Just do the three.
Buttermilk is non-negotiable for me. I know some people do the whole splash-of-vinegar-in-regular-milk trick and it probably works fine but I always have buttermilk on hand now because I make this enough to justify it. Get the real thing if you can.
For the frosting, you want blueberry jam — not jelly, not preserves with big chunks of fruit (though honestly I’ve used those and it’s fine, just a little lumpy). Regular smooth blueberry jam. That’s what gives it the color and the flavor, and you’d be amazed how much you can taste it in the finished frosting.
Fresh blueberries for the cake itself. I’ve never tried it with frozen but I suspect it would work in a pinch. You’d just want to toss them in flour while still frozen and expect a little extra purple bleeding into the batter. Probably still delicious.
Ingredients
For the Cake:
– 2 ½ cups all-purpose flour, plus 1 tablespoon for the blueberries
– 2 teaspoons baking powder
– ½ teaspoon baking soda
– ½ teaspoon salt
– ¾ cup (1 ½ sticks) unsalted butter, softened
– 1 ¾ cups granulated sugar
– 3 large eggs
– 2 teaspoons vanilla extract
– 1 cup buttermilk
– Zest of 3 lemons (don’t you dare skimp)
– 3 tablespoons fresh lemon juice
– 2 cups fresh blueberries
For the Frosting:
– ½ cup (1 stick) unsalted butter, softened
– 8 oz cream cheese, softened
– ⅓ cup blueberry jam (about — I sometimes add a little more)
– 3 cups powdered sugar
– 1 teaspoon vanilla extract
How to Make It
Preheat your oven to 350°F and grease a 9×13 baking pan well. I butter mine and then do a light flour coat because I’m paranoid about sticking, but cooking spray is fine too.
Beat the butter and sugar together until they’re pale and fluffy — this takes a solid two to three minutes with a hand mixer, maybe a little more. Don’t rush this part. I used to rush it and the texture was always slightly denser than I wanted. Now I set a little timer and walk away and do something else and come back. That’s the secret, mostly. Just leave it alone and let it do its thing.
Add your eggs one at a time, then the vanilla, then the buttermilk. It might look a little curdled after the buttermilk goes in — that’s fine, don’t panic. Add your flour mixture (I whisk together the flour, baking powder, baking soda, and salt in a separate bowl first) in two additions, stirring between each one. Then stir in your lemon juice and all that zest. The batter will smell incredible at this point. Like, almost unfairly good.
Toss your blueberries in that tablespoon of flour — this keeps them from sinking straight to the bottom of the cake, which I learned the hard way years ago — and then fold them gently into the batter. Don’t stir aggressively or you’ll crush them and turn the whole batter blue. Which, again, I’ve done. Still tastes good but you lose the distinct little bursts of blueberry.
Pour into your prepared pan and bake for 35 to 40 minutes, until a toothpick comes out clean and the edges are just starting to pull away from the pan. Let it cool completely before frosting. I mean it. I once frosted it after maybe 30 minutes because I was impatient and had people coming over and the frosting just slid right off the center in this depressing Slow drift. An hour minimum. Honestly, if you can bake it the night before and frost it in the morning, do that.
For the frosting: beat your butter until it’s really pale and fluffy, then add the cream cheese and jam and beat again until smooth. Add the powdered sugar a cup at a time — do it slowly, unless you want a powdered sugar cloud — and then beat everything on high for a minute or two until it’s light and that gorgeous purple color. Taste it. It’s honestly something else.
Spread it generously over the cooled cake. I use an offset spatula and do swoopy little peaks but you can just spread it flat if you want, it’ll still look beautiful.
Variations and Swaps
My daughter makes a version with raspberries instead of blueberries and raspberry jam in the frosting and it’s wonderful — a little more tart, the frosting comes out almost pink. She brought it to a work lunch last summer and apparently people lost their minds over it.
I’ve also added a thin layer of lemon curd between the cake and the frosting, sort of spread it on first, then frosted over it. That’s maybe my favorite version, if I’m being honest, though it’s more of a project.
If your frosting is too soft (warm kitchen, cream cheese too warm), just stick it in the fridge for 15 or 20 minutes before spreading. It’ll firm up. And if the color isn’t quite as vivid as you’d like, a drop or two of purple food coloring doesn’t hurt anything. Bea herself told me she’d done it — so that’s practically permission.
Storing It
Cover it well and keep it in the refrigerator, because of the cream cheese frosting. It’ll keep for four days, maybe five if you’re pressing it. The cake somehow gets even more moist the next day — something about the frosting sealing in the crumb overnight. I’ve eaten it cold, straight from the fridge, standing at the counter at 11pm, and I’m not embarrassed about that.
You can freeze individual slices if you want. Wrap them tight. They defrost well enough, though the frosting texture changes slightly — still good, just a little denser.
I’ve made this cake for birthdays, for just-because Tuesdays, for the time my friend Linda had her knee surgery and I wanted to bring something that felt like a real gesture. It always lands. Every single time someone asks me what’s in the frosting and I say blueberry jam and cream cheese and they get this little look on their face like that’s not a thing that should work as well as it does.
Bea’s Blueberry Sheet Cake
Ingredients
- 2 1/2 cups all-purpose flour for the cake
- 1 tbsp all-purpose flour for coating the blueberries
- 2 tsp baking powder
- 1/2 tsp baking soda
- 1/2 tsp salt
- 3/4 cup unsalted butter softened, for the cake
- 1 3/4 cups granulated sugar
- 3 large eggs
- 2 tsp vanilla extract for the cake
- 1 cup buttermilk
- 3 tbsp fresh lemon juice
- 2 cups fresh blueberries
- 3 lemons lemon zest finely grated
- 3 cups powdered sugar
- 8 oz cream cheese softened
- 1/2 cup unsalted butter softened, for the frosting
- 1/3 cup blueberry jam
- 1 tsp vanilla extract for the frosting
Instructions
- Preheat the oven to 350°F. Grease and lightly flour a 9x13-inch baking pan.
- In a medium bowl, whisk together 2 1/2 cups flour, the baking powder, baking soda, and salt.
- In a large bowl, beat the softened butter and granulated sugar for 2–3 minutes, until pale and fluffy.
- Add the eggs one at a time, beating well after each addition.
- Mix in the vanilla extract and buttermilk. The mixture may look slightly curdled.
- Add the flour mixture in two additions, mixing just until combined after each one.
- Stir in the lemon zest and lemon juice.
- Toss the blueberries with the remaining 1 tablespoon flour, then fold them gently into the batter.
- Spread the batter evenly in the prepared pan.
- Bake for 35–40 minutes, until a toothpick inserted in the center comes out clean and the edges begin pulling away from the pan.
- Let the cake cool completely for at least 1 hour before frosting.
- For the frosting, beat the softened butter until pale and fluffy.
- Add the cream cheese and blueberry jam, then beat until smooth.
- Add the powdered sugar gradually, mixing well after each addition.
- Beat in the vanilla extract, then continue beating for 1–2 minutes until light and fluffy.
- Spread the frosting evenly over the cooled cake before slicing and serving.