Instructions

1. In a mixing bowl combine egg whites and cream of tartar, beat in high speed until it forms soft peaks. Gradually add 1/2 cup of sugar until it forms stiff peaks. Set aside.
2. In a separate mixing bowl combine egg yolks, milk, the remaining sugar and salt. Mix until creamy in consistency.
3. Sift flour and baking powder then combine it with the yolk mixture.
4. Fold egg white and yolk mixture together then equally divide them into two and pour them into two rectangular greased pans (I used a 12 x 9 in pans). Bake in a 160C preheated oven for 35 minutes or until inserted toothpick comes out clean.
5. While waiting for the cake, prepare the custard by placing all Potato Custard ingredients except for egg yolks in a sauce pan. Cook in medium heat while occasionally stirring for 15 minutes or until it thickens.
6. Turn heat to low then add egg yolks, cook for 5 more minutes while constantly mixing.
7. Let the mixture cool down as well as the sponge cake.
8. Slowly remove one sponge cake from the pan and place them in a flat container. Spread potato custard on top then cover top with remaining sponge cake. Press the cake so it deflates a bit then slice them into smaller rectangular pieces. Dust it with powdered sugar then serve.