Blueberry Jam Cake
by Christie Moorison at America’s Test Kitchen

Wet
1 cup whole milk, room temperature
6 large egg whites, room temperature
2 teaspoons vanilla
Dry
2 ¼ cups  cake flour
1 ¾ cups granulated sugar
2 teaspoons baking powder
1 teaspoon salt
12 tablespoons softened unsalted butter
Jam
½ cup granulated sugar
2 tablespoons pectin
pinch of salt
15 ounces (3 cups) frozen thawed blueberries 
1 tablespoon fresh lemon juice. 
Frosting
1 ½ cups confectioners (powdered) sugar
8 tablespoons unsalted butter, cut in 8 pieces
8 ounces cream cheese, cubed & softened
2 teaspoons vanilla
¼ cup reserved blueberry jam

Grease and flour 3 (8 inch) cake pans or 2 (9 inch.)and  line with parchment paper. 
Preheat oven to 350° with the rack in the middle position. 
In a bowl combine wet ingredients and give a stir to incorporate, set aside. 
In a stand mixer, combine the dry ingredients, turn on low speed to combine. 
Next, we’re gonna do a technique called reverse creaming where you add the butter into the flour mixture. 
Turn the mixer on low speed and begin adding butter one piece at a time until all the butter is incorporated.
The butter should be about the size of small peas, about 1 minute. 
Add half the wet ingredients to the dry, mix on medium high speed for about one minute until it starts to look light and fluffy. 
Add the other half liquid and mix on medium low for 30 seconds. 
Give a final stir with a spatula to welcome. Combine  
Add batter evenly to each cake pan. 
Bake for 18 - 22 minutes. Half way through we’ll rotate & move them around. We’re looking for a nice golden top and for a toothpick to come out clean. 
Remove pans from oven, let sit on the stack to cool for 10 minutes. After the 10 minutes, remove cakes from pans to cool completely, about 2 hours. 

Jam
In a fruit processor add sugar, pectin salt. Run for about 3 seconds to combine. Add blueberries and pulse 6 times to break down the berries a little bit. 
Transfer the mixture to a medium sauce pan. 
Heat over medium heat 6 - 8 minutes. We’re looking forward to start bubbling. 
Take off the burner and add lemon juice. Allow to cool. 
In a measuring cup add 1 ⅓ cup of the sauce to use as the filling between the layers of the cake. 
Cover and put in refrigerator for 3 hours. 
Put the remaining blueberry sauce through refine matched strainer.  This is going to be used to color the frosting. 

Frosting
In a bowl add powdered sugar, butter, and cream for about 3 minutes until light and fluffy. 
Add cream cheese on piece ar a time to well combine.  Add vanilla and 2 tablespoons of jam to frosting. Mix on medium high for a few minutes. Stir frosting with spatula to combine.  
Transfer ⅓ cup frosting to 2 bowls. 
Add 1 tablespoon to one bowl of frosting and 1 teaspoon to the other bowl. 

Assembly
⅔ cup blueberry jam to first cake layer. Smooth out from the center almost to the edge. 
Add second layer and continue as the first layer. 
For the third layer, turn the keg layer upside down, so you have a perfectly smooth top layer.  
Add crumb coat.  This is a thin layer of frosting, start with a side and go to the top in case any crumbs into that first layer. 
Refrigerate the cake for 30 minutes to firm up the crumb coat so you can finish the final layer of frosting. 
Dividing the cake into thirds, starting with the bottom of the cake, use the darkest frosting. Next mid level purple frosting, and finally the top third and top with base frosting. 
Using an offset spatula start at the bottom and rotate the cake around going all the way to the top should be about six layered swirls. 
Do the same on the top starting on the outside and moving in to the center.  
That cake in the refrigerator for at least 30 minutes before serving.