Lemon-Blueberry Layer Cake

INGREDIENTS

For the Blueberry Jam:

1 lb

blueberries (about 2½ cups)

1/2 cup

sugar

For the White Cake:

1/2 cup

butter, room temperature

1 1/2 cups

sugar

egg whites, room temperature

2 tsp

vanilla extract

2 cups

flour

1 tsp

baking powder

1/2 tsp

baking soda

1/4 tsp

salt

1 1/3 cups

buttermilk, room temperature

For the Lemon Buttercream:

2 cups

or 1 lb) unsalted butter, room temperature

2 lb

confectioners' sugar, sifted (8 cups)

Tb fresh lemon juice

1 tsp

lemon extract

to 2 Tb milk to reach desired consistency if needed