Step 1

Preheat oven to 325°F (163°C). Grease the inside of a 7 inch round cake pan with a cooking oil spray and line the bottom with parchment paper. Do not line the sides but make sure they are greased. Use a solid one-piece cake pan (no removable bottom).

Step 2

Add yogurt, condensed milk and egg yolks to a large mixing bowl. Whisk until ingredients are fully incorporated and you have a smooth batter.

Step 3

Whisk in lemon juice and zest.

Step 4

Add egg whites to a large mixing bowl. Beat at highest speed until stiff peaks form. Add one third of the egg white mixture to the egg yolk batter. Fold it in gently with a spatula until no egg white lumps remain. Make sure you scoop up batter from the very bottom of the bowl each time you fold to make sure all of the batter gets incorporated with the egg whites. Repeat with the next 1/3 and then the remaining 1/3.

Step 5

Pour batter into the prepared baking pan. The cake will be baked in a water bath. To do this, place your cake pan into a slightly larger baking pan. I used a 9 x 9 inch baking pan. Make sure to use a pan that is only slightly larger than the pan the cake is baking in so that there is not too much water added. Place your cake pan into the bigger pan. Pour just enough cold tap water into the outer pan so that the water level reaches 5/16 inch. Use a ruler to measure the water to ensure you only have up to 5/16 inch. If your water level is too high, the bottom of your cake will cook too much, causing a dense bottom layer.

Step 6

Place cake with water bath into your oven. Bake for 45 minutes or until top of cake is browned and looks done. (Check on the cake through the oven window and don't open the oven door. You just want the top of the cake to look cooked.) Turn off the oven but do not open the oven door and leave the cake in the oven for one hour. It is important to leave the cake in the oven (unopened) because this allows the cake to finish cooking and the gradual drop in temperature prevents the cake from suddenly collapsing. The cake will shrink down, but it shouldn't completely collapse. After one hour, you can remove the cake from the oven. Let the cake cool to room temperature. Place cake uncovered into fridge for several more hours or overnight. This helps the cake develop a better flavor and will remove some of the excess moisture. If desired, dust top with powdered sugar before serving.