Lemon Meringue

I made lemon meringue pie over the weekend with a super easy recipe.  I really just wanted the meringue part, but felt it necessary to put the meringue on top of something.

You will need for the filling
1 can of sweetended condesned milk
1/2 cup lemon juice
some lemon zest
3 egg yolks (save the whites)

You put this all together and put it in a pie shell of your choice. 

For the meringue you will need
3 egg whites
1/4 teaspoon cream of tarter
1/4 cup sugar

You beat the whites and the COT together until soft peaks form and then slowly beat in the sugar.  You put this meringue on top of the filling. 

Now the recipe says to cook for 12 - 15 minutes at 325, but this did not do it for my pie.  It came out really watery and did not set properly.  Then I went back and read the reviews and a lot of people had this complaint.  They suggested cooking the filling first, and then putting the meringue on top and cooking it all again.  And also then putting it in the fridge to set.   I would like to try this again cooking the filling first on its own, because it was super easy and the flavor is good, it just didn't set properly. I know most lemon meringue uses corn starch though or something for it to set....