Lemon poppy seed cake

Cake:
3 cups (420g) cake flour*
2 cups (400g) caster sugar
4 ½ teaspoons baking powder
½ teaspoon salt
3 tablespoons poppy seeds
1 cup (2 sticks/226g) unsalted butter, room temperature, coarsely chopped
grated zest and juice of 1 large lemon
1 ¼ cups (300ml) buttermilk
5 egg whites
1/3 cup (80ml) water

Vanilla cream cheese frosting:
2 vanilla beans
5 cups (700g) confectioners’ sugar, sifted
224g (8oz) cream cheese, room temperature
1 cup (226g/2 sticks) unsalted butter, room temperature
1 tablespoon vanilla extract

Preheat the oven to 180°C/350°F. Butter three 20cm (8in) round cake pans. Line the bottom of each with a round of parchment paper and butter the paper.

Combine the flour, 1 ¾ cups (350g) of the sugar, baking powder, salt and poppy seeds in the large bowl of an electric mixer. Beat on low speed to blend the ingredients and break up any lumps, about 30 seconds. Add the butter, lemon zest and 1 cup of the buttermilk to the flour mixture. Beat on low – be careful, the flour may fly everywhere – until completely mixed. Raise the speed to medium and beat for 1-2 minutes to lighten and aerate the batter.

In a medium bowl, combine the egg whites with the remaining ¼ cup buttermilk; whisk to blend thoroughly. Add this mixture to the batter in 2-3 additions, scraping down the sides of the bowl and beating only enough to incorporate. Divide the batter among the prepared pans.
Bake for 25-30 minutes or until a toothpick inserted in the center comes out clean. Let the cakes cool in the pans for 10 minutes.

While the cakes are cooling, make the lemon syrup: in a small nonreactive saucepan, combine the remaining ¼ cup (50g) of sugar, the lemon juice and the water. Bring to the boil, stirring to dissolve the sugar. 

Turn out the cake layers onto wire racks and generously brush them hot lemon syrup over the warm cakes to moisten evenly. Let cool completely.

Make the frosting: split the vanilla beans lengthwise and scrape the seeds into the sugar with the back of a knife. In the large bowl of an electric mixer, beat the cream cheese and butter on medium speed until light and fluffy. Gradually add the sugar, 1 cup at a time, beating well after each addition and scraping down the sides of the bowl. Continue to beat until very fluffy, 3-4 minutes. Add the vanilla extract and beat well.

Original recipie here & here.