Separate the egg yolks and egg whites into separate bowls.

In a pot over low heat, melt the butter, cream cheese, and 1/4 cup of fine sugar, mixing until smooth.

Remove the pot from heat and add the egg yolks to the mixture, mixing gently.

Add the corn starch and flour to the mixture; mix until clumps disappear.

Add the milk and any optional flavorings; mix until smooth.

Preheat the oven to 330?F (165?C) and prepare a bain-marie with water in a deep baking pan.

Line the baking pans with parchment paper.

Beat the egg whites into stiff peaks.

Mix a portion of the beaten egg whites into the batter, then fold in the remaining egg whites.

Pour the batter into the prepared baking pans.

Bake in the bain-marie for 25 minutes at 330?F (165?C).

If the cake hasn?t risen, adjust the temperature and allow to rise, then crack the oven door slightly and lower the temperature to 245-265?F (118-130?C). Bake for an additional 45 minutes.

Rest the cake in the oven for 10 minutes after baking.

Invert the cake onto a plate, remove the parchment paper, and flip again onto a serving plate.