In a small saucepan, add 10 oz. guava paste and ½ cup water. Over medium heat, melt the guava paste, occasionally stirring until a thick sauce forms without clumps. Set aside to cool.
In the bowl of a standing mixer fitted with the paddle attachment, or with a hand-held mixer, beat together 3 packages of softened cream cheese with 1 cup sweetened condensed milk until smooth. Add 2 tablespoons of lime juice and half of the guava sauce (about ¾ cup). Mix to combine.
Spray an 8-inch springform pan with non-stick cooking spray or oil. Arrange Marias cookies in a single layer on the bottom and sides of the pan. Pour ⅓ of the filling over the cookies, making sure they are completely covered. Repeat the layering two more times, finishing with the filling on top.
Evenly spread the remaining guava sauce over the filling and refrigerate for at least two hours or until set. Open the springform pan and remove the ring. Cut the cake into wedges and serve with whipped cream if desired.
Refrigerate the leftovers.
Use an offset spatula to spread filling evenly across the cookies, as you don't want it pooling up in one area. You want a beautiful, level surface for the next layer of cookies.
You want the filling to get really cold and firm, all the while softening the cookies so you can slice through them with ease when your wait is finally over.
To cut the cake, warm your serving knife under hot water, dry it off, then make a clean slice. Do this for each cut.