Bea’s Blueberry Sheet Cake
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Ingredients
For the cake: 3 cups allpurpose flour, plus 1 tablespoon set aside for the berries 2 teaspoons baking powder 1 teaspoon baking soda ½ teaspoon salt 1 cup (2 sticks) unsalted butter, softened — really softened, not just slightly less cold 1½ cups granulated sugar 4 eggs, room temperature 2 teaspoons vanilla extract 1 cup buttermilk, room temperature Zest of 3 lemons (I eyeball this — be generous) ¼ cup fresh lemon juice, about 2 lemons 1½ heaping cups fresh blueberries
For the frosting: ¾ cup unsalted butter 6 oz cream cheese, room temperature — this matters, don’t rush it ¼ cup blueberry jam 3 cups powdered sugar 1 teaspoon vanilla
Let’s Make It
Preheat your oven to 350°F and get your 9×13 ready. I grease mine well and also line it with parchment when I’m planning to serve it at something — if I’m just leaving it in the pan for the family to pick at, I skip the parchment. Either way is fine.
Whisk your dry ingredients together in a bowl and set them aside. In your stand mixer — or a big bowl with a hand mixer, I’ve done it both ways — cream the butter and sugar until it’s genuinely light and fluffy. This takes longer than you think. Give it a real 23 minutes. Add the eggs one at a time, then the vanilla, and mix until combined. Pour in the buttermilk slowly with the mixer on low. The batter might look a little curdled at this stage and that’s okay, it comes together.
Add the dry ingredients in two additions — don’t dump it all in at once, I’ve done that when I’m in a hurry and the flour goes everywhere — and mix until just combined. Then add your lemon juice and zest. Toss the blueberries with that reserved tablespoon of flour first. This is one of those steps that feels fussy but it genuinely helps keep the berries suspended in the batter instead of sinking. Fold them in gently.
Pour into your pan and bake for 4045 minutes. Mine usually needs the full 45, sometimes a minute or two more — ovens vary wildly, mine runs a little cool, I’ve never fully trusted it since we moved and I keep meaning to get an oven thermometer and forgetting. Check it with a toothpick in the center. Let it cool completely before frosting. Completely. Do not rush this. A warm cake will melt your frosting and you’ll be sad.
While it cools, make the frosting. Whip the butter in a mixing bowl until it’s pale and fluffy — this takes a good 58 minutes and it’s worth it, don’t stop early. Add the cream cheese and beat until it’s fully incorporated and smooth. Mix in the jam. Then add the powdered sugar a little at a time on low — if you dump it in fast you’ll be covered in a cloud of sugar, ask me how I know — and once it’s all in, add the vanilla and crank the speed up and whip for another couple minutes until it’s light and beautiful and that color. That gorgeous, improbable color.
Spread it over the cooled cake. I use an offset spatula and make swirly swoops. You could scatter a few fresh blueberries on top for looks, though I don’t always bother.
Bea’s Blueberry Sheet Cake
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Variations
You can swap the blueberries for raspberries and use raspberry jam in the frosting — the pink is even more dramatic. I once tried making it with blackberries because that’s what I had and it was delicious but the frosting turned a color that I can only describe as grayishpurple, which tasted incredible but looked a little alarming. If you’re taking this somewhere, stick with blueberry.
You could do this with a lemon curd swirl in the batter instead of the juice, though I haven’t tried it myself. Someone in the comments on some food site suggested it once and I’ve been meaning to experiment. One of these days.
Keeping It
The cake keeps fine on the counter, loosely covered, for about two days. After that I’d refrigerate it — the cream cheese in the frosting makes me nervous past 48 hours unrefrigerated, though honestly I’ve never had a piece last that long without disappearing. From the fridge it’ll keep for four or five days. Let it come to room temperature before eating if you can — cold cake is okay but roomtemperature cake is the version that made you fall in love with it in the first place.
I don’t freeze it. I’ve heard of people freezing frosted cake slices and I respect the ambition but I’ve never done it with this one. Seems like it would change something.
One more thing — the lemon flavor in this cake is bright without being puckery. It works with the blueberry instead of competing with it, which is exactly what you want.
Slice it into whatever size you want. I cut mine smaller than I probably should and then go back for another piece, which I think is the correct way to eat a sheet cake anyway.
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