For the cake

1. Heat oven to 350 degrees. Butter and flour a 9×13 inch baking dish. Set aside.
2. In a small bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
3. In the bowl of an electric mixer fitted with the whisk attachment, beat the egg whites for about 30 seconds, then gradually add the sugar. Increase speed to medium-high and continue beating until stiff peaks form, 4-5 minutes. Add egg yolks 1 at at time, beating well after each addition. Add flour mixture, water, and almond extract. Mix on slow speed until evenly blended.
4. Pour batter into prepared pan and bake 30 to 40 minutes or until a cake tester inserted into the cake comes out clean. Cool cake while making the milk mixture.

For the milk mixture

1. In a medium saucepan, whisk together all the ingredients for the milk mixture. Heat mixture to boiling over medium-high, whisking constantly. Let mixture cool slightly. Reserve 1/2 cup of milk mixture for serving. Once cake is lukewarm to the touch, pierce cake all over with a fork. Pour remaining milk mixture over cake, 1 cup at a time. Allow the milk mixture to absorb into the cake between additions. Gently tilt the pan as necessary to evenly distribute the milk mixture.
2. Cover the cake and refrigerate overnight.

For the frosting

1. Beat cream with granulated sugar until stiff peaks form. Add sour cream, powdered sugar, vanilla and Frangelico, if using. Beat until evenly mixed. Spread frosting over cooled cake.
2. Keep cake refrigerated until ready to serve. Cut cake into squares. Spoon some of the reserved milk mixture onto serving plates and top with a piece of cake.