Step 1

Preheat the oven to 350° F (180° C).

Step 2

In a bowl add the 4 egg whites, saving the yolks for later. With an electric mixer, beat the egg whites for a few minutes until doubled in size.

Step 3

Add the cup of sugar and beat a few more minutes. Add the egg yolks while beating. Beat in the teaspoon of vanilla extract and the butter (soften).

Step 4

Sift in the flour, corn starch and baking powder.

Step 5

Add the finely grated zest of one lemon.

Step 6

And beat until just combined.

Step 7

Grease or line with parchment paper a 9x13 inch (23x33 cm) baking pan. Pour the batter and level with a spoon.

Step 8

Bake in the preheated oven for 20 minutes or until done.

Step 9

Remove from the oven and let it cool while you prepare the milk cream.

Step 10

In a large bowl, add the whipping cream and the tablespoon of powdered sugar. Whip to stiff peaks (possibly using a whisk attachment to an electric mixer)

Step 11

Add the vanilla extract and condensed milk, and whip some more.

Step 12

When cold, cut the cake in half horizontally.

Step 13

Place the top half, top-down back in the pan with parchment paper. The paper will help you to remove the cake from the pan later.

Step 14

Add the cream and level with a spatula.

Step 15

And carefully top with the bottom half of the cake.

Step 16

Refrigerate for at least an hour, or until ready to serve.

Step 17

Sprinkle with powdered sugar and cut into your desired size.

Step 18

I made 12 rectangular bars. Each about 2 by 4.5 inches, but you're welcome to cut these as you wish.

Step 19

Store in the refrigerator for up to 3 days.