Lemon Buttermilk Cake

2 1/2 C. cake flour

1 tsp. baking powder

1/2 tsp. baking soda

1/2 tsp. salt

3/4 C. buttermilk, room temperature

3 T. grated lemon zest (about 3 lemons)

1/4 C. fresh lemon juice

1 tsp. vanilla extract

1 3/4 C. granulated sugar

12 T. (1 1/2 sticks) unsalted butter, softened

3 large eggs plus 1 egg yolk, room temperature

 

3 C. confectioners’ sugar

3 T. lemon juice

2 T. buttermilk

 

Adjust oven rack to middle position. Heat oven to 325 degrees. Grease and flour a glass 13 x 9-inch baking pan. Combine flour, powder, soda and salt in a medium bowl. Combine buttermilk, lemon juice and vanilla. Beat granulated sugar and lemon zest until moist and fragrant, about 1 minute. Reserve 1/4 C. of sugar mixture; cover and set aside. Add butter to remaining sugar mixture and beat until light and fluffy, about 2 minutes. Add eggs and yolk, one at a time, until incorporated. Reduce speed to low. Add dry ingredients in 3 additions, alternating with buttermilk mixture in 2 additions. Mix until smooth about 30 seconds. Scrape batter into prepared pan an smooth top. Bake until cake is golden brown and toothpick inserted into center comes out clean, 25 to 35 minutes. Transfer cake to wire rack and let cool 10 minutes. For the glaze: While cake cools, whisk confectioner’s sugar, lemon juice and buttermilk until smooth. Gently spread over warm cake. Sprinkle evenly with reserved sugar. Cool completely, at least 2 hours.