Myrna's 67th Birthday Cake

My mother requested "Grandma Forbes' sponge cake" for her birthday today. The cake recipe was her grandmother's; apparently Grandma Forbes baked it every year and mailed it to her daughter, my mother's Aunt Pearl (quite an ordeal in those days). Grandma Forbes died in 1958, and Mother has fond memories of eating this cake in her childhood. She made hers in a 9x13 sheet pan, but I gussied this one up with layers of limoncello pastry cream filling and a whipped cream frosting. The gelatin in the cream stabilizes the frosting and filling so that you can enjoy the cake the following day.

Cake:
2 cups flour
2 cups sugar
2 tsp baking powder
1/2 tsp salt
1 cup boiling water
1 tsp vanilla extract
7 egg whites

Stir together flour, sugar, baking powder and salt. Set aside.

Whip egg whites to stiff but not dry peaks. Whisk boiling water and vanilla extract into dry ingredients. Fold into egg whites. Divide between three 8" round pans with parchment-lined bottoms. Bake at 350 degrees for 25 minutes or until cake springs back when pressed in center. Cool on racks.

Filling and Frosting:
4 egg yolks
2 Tbsp flour
2 Tbsp cornstarch
1/4 tsp salt
1/3 cup sugar
1 1/3 cups milk
3 Tbsp limoncello liqueur
2 tsp lemon extract
1 Tbsp cold water
1/2 tsp unflavored gelatin
2 c heavy whipping cream
3 Tbsp confectioners' sugar
1 1/2 tsp vanilla extract

Beat egg yolks, sugar, flour and cornstarch on high speed until thick and pale yellow, about 2 minutes. Set aside.

Heat milk to a simmer, then whisk milk slowly into egg mixture until about one-third is incorporated. Scrape egg mixture back into pan with milk. Cook over medium-low heat, whisking constantly and scraping the bottom and corners of the pan until thickened and beginning to bubble. Cook a minute longer, then scrape into a clean bowl with a clean spatula. Press a piece of parchment paper onto the surface of the custard to prevent a skin from forming. Cool completely.

Put cold water in a heatproof cup. Sprinkle gelatin atop, then let stand 5 minutes without stirring. Place the cup in a saucepan of simmering water until gelatin melts clear. Let cool to room temperature.

Whip cream to soft peaks, drizzling gelatin mixture in as cream begins to thicken, then adding sugar and vanilla. Stir about 3/4 cup of whipped cream into limoncello custard until incorporated, reserving remainder of whipped cream for frosting.

To assemble, spoon limoncello custard evenly between layers of cake, spreading to within 1/2" of edge. Top liberally with whipped cream, swirling with an offset spatula. Makes approximately 12 servings.