Blueberry Birthday Cake

Being a Navy family has meant we have to celebrate when Uncle Sam makes it convenient. Poor Meatball has spent 2 of his 6 birthdays (one and four) moving across the country. Deployments, PCSing, and work travel have made us pretty flexible as to the when of our birthdays, but one thing is certain, the birthday boy gets to pick what kind of cake he wants and I bake it.

Wombat’s cake (which we enjoyed three days after his actual birthday because he was on travel) was a challenge: blueberry cake with vanilla frosting. Two years ago he asked for vanilla cake with blueberry frosting, which was, ahem, a piece of cake. I went to my Cake Bible to search for a recipe, because Rose Levy Beranbaum is a genius of pastries. No luck. I then turned to Pinterest, and while I love Pinterest, recipes tend to shout “Easy!”, “Fast!”, or “Three-Ingredient Recipe!” with the first ingredient being a box of cake mix. I’ll own up to my snobbery, but with very few exceptions I don’t bake from mix, so I returned to the Cake Bible. I thought about mixing blueberries into a vanilla cake, but that’s pretty much a blueberry muffin, which, while delicious, isn’t exactly celebratory. I wanted a more homogenous blueberry flavor and an even texture (and didn’t want Peanut picking whole blueberries out of his cake). My go-to buttercream recipe can be flavored with fruit butter or puree, and I wondered if I could doctor a cake recipe the same way. I knew I’d have to balance moisture, structure, and sweetness but since I was working from a baking powder leavened recipe, I figured acidity wouldn’t be as critical.

Using blueberry jam as my flavoring, I’d reduce the milk and sugar accordingly, and to support the structure that could be compromised by using jam in place of some of the sugar, I used whole eggs in place of some of the egg whites. This also simplified the process (to offset what comes next).

Then, like the geek I am, I mathed. Also, I guessed. The total mass of milk and sugar was 542 g and I decided I could get away with swapping a third of that for jam, so I would use 180 g jam, which, with 13 g of sugar in every 20g of jam, would contribute 117 g of sugar. So I subtracted that from the 300g sugar called for in the recipe, 183g in the new formula.  Milk would be reduced from 242g to 180. (teachers, feel free to use this for the next time a student asks “when are we ever gonna use this?”)

This will probably work with any fruit jam, but I would use seedless when possible, blackberry and raspberry seeds can be quite obtrusive.

So, the final ingredient list:

• 2 large eggs plus 1 egg white (about 135 grams)
• 180g milk (about 3/4 cup)
• 2 1/4 teaspoons vanilla
• 300g cake flour (3 cups)
• 180g sugar
• 1 tbsp plus 1 tsp baking powder
• 1/4 tsp salt
• 12 tbsp unsalted butter, which MUST be softened. Seriously. I leave my butter out the night before baking to make sure it’s soft enough. Alternatively, you can fill a large bowl with boiling water, let it sit for a minute, pour it out, then invert the warm bowl over the butter. If you have a butter scavenging dog like my friend Jenny, this method is best.
• 180g blueberry jam

Preheat oven to 350F. Grease 2 9-inch cake pans, line the bottoms with parchment, then grease the parchment and flour the bottom and sides.

Mix the eggs and white, 45 g of the milk, and about half the jam together in a bowl. I use a glass measuring cup for this because that’s easier for pouring it into your mixer bowl later.

Mix the dry ingredients together for about 30 seconds to blend. Add the butter and remaining milk and jam and mix on low until all ingredients are moistened so you don’t get a face full of flour when the real mixing starts (THIS is why the butter has to be soft, there is no creaming step to beat it into submission). Increase to medium speed and beat for 1 1/2 minutes. Scrape down the sides. Gradually add the egg mixture in three batches, beating for 20 seconds after each addition.

Scrape the batter into the prepared pans and smooth the surface. Bake 20-25 minutes, let cool on a rack for 10 minutes, then loosen the sides with a knife or spatula and invert onto greased racks before reinverting so the tops are up. This prevents the layers from splitting. Cool completely.

On to the buttercream. Oh, the buttercream. It should be written BUTTERcream. Go ahead and lose any sense of virtue you may have gained from putting fruit in the cake because we’re about to get down with an entire box of butter.

Vanilla Buttercream (from the Neoclassic Buttercream recipe in The Cake Bible)

• 6 egg yolks
• 3/4 cup sugar
• 1/2 cup corn syrup
• 2 cups (yup that’s FOUR sticks, one POUND) unsalted butter, softened
• 2 tsp vanilla

A handheld electric mixer is ideal for this recipe, but it can be done with a stand mixer. I use my stand mixer because we somehow have 2 handheld mixers but not a matching pair of beater attachments for either.

Beat yolks until light in color. Have a greased heatproof glass measuring cup ready.

Combine corn syrup and sugar in a small saucepan and heat while stirring constantly until the sugar dissolves and the syrup comes to a full rolling boil. Immediately transfer to the glass measuring cup.

If you’re using a handheld mixer, beat the yolks with one hand while steadily and slowly pouring the sugar syrup into the bowl. With a stand mixer, pour a small amount of syrup into the bowl and immediately beat oh high for 5 seconds. Stop the mixer and add a larger amount of syrup, beating again, continuing in this manner until you’ve scraped the last of the syrup from the measure.

Continue beating until completely cool. This takes a while, so maybe the stand mixer isn’t so inconvenient after all.

Gradually beat in the butter and vanilla. I cut the butter into 1-2 tbsp sized chunks and add one or two at a time and when they disappear I add more. The frosting will look too runny for a long time but don’t panic, it will eventually resemble a silky, fluffy buttercream. I still panic. Every. Single. Time.

We have somehow found ourselves with two open but almost full jars of seedless blackberry jam in our fridge, so I know what I’m going to try next. With lime buttercream!