In a large mixing bowl, combine your cream cheese, sweetened condensed milk, sour cream, vanilla extract and corn starch. Mix until all ingredients are well incorporated.
Next, separate your egg yolks from the egg whites. Add your egg yolks one at a time to your cream cheese mixture while mixing. Make sure your ingredients are well-combined.
In a separate bowl, beat your egg whites until stiff peaks form when you lift your mixer from the bowl. This may take between 5-7 minutes depending on the speed in which you are mixing.
Using a spatula, gently fold your egg whites into your cheesecake filling. Do not mix!
Immediately pour your cheesecake filling into your pre-baked crust.
Scoop 1 tablespoon at a time of the guava marmalade onto the top of your cheesecake.
Once finished, immediately use the tip of a knife to make swirl patterns of your choice. This step should be done right away so the guava marmalade does not sink into the cheesecake. Making the guava swirls is completely optional and just makes the cheesecake look a little bit prettier. Plus, it helps to spread the guava marmalade all over the top of your cheesecake.
Next, add 1 inch of water to a large baking pan and place your spring form pan with the cheesecake inside of it. This is called a water bath and will ensure your oven retains moisture which is a great environment for your cheesecake to bake in.
Bake in a preheated oven at 325 degrees F for 40-45 minutes.
Finally, remove your guava cheesecake from the oven and allow it to cool down on your counter top for about 1 hour. Once it has reached room temperature, allow it to finish cooling inside the refrigerator for a minimum of 4 hours or overnight.