Lemon Cake with Blueberry Buttercream

Today I made my first gluten-free layer cake! Unfortunately, you can't quite see the layers where I split and filled them, but it tastes great all the same.

I based this off of the recipe for Lemon Layer Cake from Gluten Free Baking Classics. I made a few subtle changes to get the layers as flat as possible, and replaced the lemon American-style buttercream with a blueberry Italian buttercream. As always, my changes are in bold.

But first, pictures!



My trusty mixer!

The prepared pans

Look how nice and flat! You can also see the fabric tied around the pan.

The finished cake!

Big slice missing....

Yum!

Recipes here:

Lemon Layer Cake
Makes two 8 or 9 inch rounds or 24 cupcakes.  Recipe can be cut in half.  

2 cups sugar
4 large eggs
2 1/2 cups Brown Rice Flour Mix*
1/2 tsp salt
1 Tbsp baking powder
1 tsp xanthan gum
1 cup canola oil
1 cup milk
1 tsp pure vanilla extract
1 tsp pure lemon extract (I used 1.5 teaspoons)
1 Tbsp grated lemon rind.
Lemon Curd Filling and Lemon Buttercream Frosting (recipes follow)

Preheat oven to 350 degrees (I baked at 325 instead).  Position rack in center of oven.  Line two round 9-inch layer cake pans with parchment or wax paper and spray lightly with cooking spray (only sprayed bottom - not sides). Soak long strips of fabric in water, wring out the excess, and tie around the baking pans -- this helps prevent a dome from forming.

Beat sugar and eggs in large bowl of electric mixer at medium speed for 1 minute.  Add flour, salt, baking powder, xanthan gum, oil, milk, vanilla extract, lemon extract, and lemon rind; beat at medium speed for 1 minute.

Pour batter into prepared pans.  Drop the pans from 5 inches a few times to help release any air bubbles. Place in center of oven and bake about 35 minutes (40 minutes for an 8-inch cake; 18-20 minutes for cupcakes) (I baked at 325 for 50 minutes) or until center springs back when touched and cake has pulled away from sides of pan.
Cool cake layers in the pans on a rack for 5 minutes.  Use a small knife to cut around pan sides to loosen cake.  Invert cake layers onto a rack, peel off paper, and cool completely. I placed my layers in the freezer, tightly wrapped in plastic wrap. This makes it easier to split the layers.

Carefully slice each layer in half horizontally to create four layers (this is more easily done when cake has been chilled).  Spread each of the two bottom layers with 1/2 of the lemon curd.  Cover each bottom layer with one of the two remaining top layers.

Place one set of filled layers on a cake plate and spread with about 1/2 cup frosting.  Place the other set of filled layers on top and cover top and sides of cake with remaining frosting.

Lemon Curd Filling
3 eggs yolks
1/4 cup plus 2 Tbsp sugar
1/4 cup fresh lemon juice
1/4 cup unsalted butter, cut into 4 pieces
1/4 tsp guar gum
2 tsp grated lemon rind
1/4 tsp lemon extract

Combine egg yolks, sugar, and lemon juice in a small saucepan and whisk until well blended.
Cook over medium-low heat until smooth and so thick that curd coats the back of a wooden spoon (this should take 5-7 minutes).  Whisk in butter, one piece at a time, until completely incorporated.  Whisk in guar gum, lemon rind, and lemon extract. 

Pour (I strained the curd through a very fine sifter) the curd into a small bowl and cover with wax paper or plastic wrap.  Chill until very cold.

Then, I made an Italian buttercream. This is much less sweet than the usual buttercreams, though is still very rich.

Blueberry Buttercream 

1 1/3 cups sugar (+ 1 Tbsp, separated)
1/2 cup water
4 eggs whites
1/4 tsp salt
2.5 sticks butter (1 1/4 cups)
a splash of vanilla extract
1 cup fresh blueberries, pureed (I added a few tablespoons of powdered sugar, because the blueberries weren't very sweet)

Heat up the sugar and water in a saucepan until 240 degrees (soft ball stage). While the sugar is boiling, beat the egg whites, salt, and remaining Tbsp sugar at high speed until soft peaks form. Let stand until sugar mixture is ready.

Once the sugar has come up to temperature, turn the mixer to a medium speed. Add the sugar mixture to the egg whites in a steady stream directly from the pan. Beat for 10 minutes, or until cool. At this point, you have a boiled meringue frosting.

Add the butter a tablespoon at a time, letting it incorporate fully before adding the next piece. Make sure to add all of the butter -- I know it seems like a lot, but adding less than the full amount will leave the buttercream a soupy mess (trust me, I tried).

Once the buttercream is smooth, switch to the paddle attachment and add the pureed blueberries. You could add more pureed blueberries for a stronger color or flavor.

I layered the cake as follows (from the bottom to the top):
Cake
Lemon curd
Cake
Lightly sweetened pureed blueberries (with a dam of buttercream piped around the outside)
Cake
Lemon curd
Cake
Blueberry Buttercream

For next time, I think that I will bake the cake for a bit longer. It is almost too moist, though that may improve by tomorrow. But for my first gluten-free layer cake, I think it turned out really well!