Lemon Curd: In a stainless steel bowl placed over a saucepan of simmering water, whisk together the eggs, sugar, and lemon juice until blended. Cook, stirring constantly (to prevent it from curdling), until the mixture becomes thick (like sour cream or a hollandaise sauce) (160 degrees F or 71 degrees C). This will take approximately 10 minutes. Remove from heat and immediately pour through a fine strainer to remove any lumps. Cut the butter into small pieces and whisk into the mixture until the butter has melted. Add the lemon zest and let cool. The lemon curd will continue to thicken as it cools. Cover immediately (so a skin doesn't form) and refrigerate until cold. The lemon curd can be made several days (up to a week) in advance.

Preheat oven to 350 degrees F (177 degrees C). Butter and flour, and then line the bottoms with parchment paper (or spray with Bakers Joy), two - 9 inch x 1 1/2 inch (23 x 3.75 cm) cake pans. Set aside.

Coconut Cake: While the eggs are still cold separate the eggs, placing the yolks in one bowl and the whites in another bowl. Cover the two bowls with plastic wrap and allow the eggs to come to room temperature before using (about 30 minutes).

In a mixing bowl sift or whisk together the flour, baking powder, baking soda, and salt. Set aside.

In bowl of electric mixer, or with a hand mixer, beat the butter until soft (about 1-2 minutes). Gradually add 1 1/2 cups (300 grams) of the sugar and beat until light and fluffy (about 2-3 minutes). Add the egg yolks, one at a time, beating well after each addition. Scrape down the sides of the bowl. Add the vanilla extract and beat until combined.

In a small bowl whisk together the buttermilk and coconut cream (if using).

With the mixer on low speed, alternately add the flour mixture and buttermilk mixture, in three additions, beginning and ending with the flour.  

In a clean bowl of your electric mixer, with the whisk attachment, (or with a hand mixer) beat the egg whites until foamy. Add the cream of tartar and continue beating until soft peaks form. Gradually add the remaining 1/4 cup (50 grams) of sugar and continue to beat until stiff peaks form. With a rubber spatula gently fold a little of the whites into the batter to lighten it, and then fold in the remaining whites until combined. Do not over mix the batter or it will deflate.

Divide the batter and pour into the prepared pans, smoothing the surface with an offset spatula or the back of a spoon. Bake for about 35 to 40 minutes or until a toothpick inserted into the center of the cake comes out clean and the cake springs back when pressed lightly in center.  

Place the cakes on a wire rack to cool, in their pans, for about 10 minutes. Then invert the cakes onto a greased rack. To prevent splitting, reinvert cakes so that tops are right side up. Cool completely before filling and frosting.

Frosting:  In a stainless steel bowl over a saucepan of simmering water, place the egg whites, sugar, water, and corn syrup. With a handheld electric mixer beat the mixture for 3 to 4 minutes on low speed. Increase the speed to high and continue to beat for another 3 to 4 minutes or until the icing is shiny and satiny with soft peaks.

Remove from heat, add the vanilla extract, and continue to beat on high speed for another 1 to 2 minutes or until the frosting is thick. Use immediately.

Assemble:  With a serrated knife, cut each cake layer in half, horizontally. Place one cake layer on your serving plate and spread with about 1/3 of the lemon curd and 2 tablespoons of coconut. Continue with the next layers, stacking and filling with the lemon curd and coconut. Frost the top and sides of the cake with the 7-Minute Frosting and then sprinkle with about 1 cup of coconut. Cover and refrigerate the cake until serving time.

Makes one - 9 inch (23 cm) layer cake.

Sources:

Foster, Sara. 'The Foster's Market Cookbook'. Random House. New York: 2002.