1. In a medium saucepan over medium heat, whisk together first 5 ingredients (through salt), adding to the pan in the order listed. Cook until bubbly (about 10 min.), stirring regularly at first, then whisking constantly for the last 5 min.
2. Continue cooking until mixture boils (about 2 min. more), whisking the entire bottom of the pan constantly, including the corners, to avoid scorching and lumps. Boil for 1 min.
3. Remove from heat; whisk in vanilla and butter.
4. Transfer to a heatproof bowl; cover with plastic wrap touching the surface of the pastry cream. Chill completely in the refrigerator for at least 4 hrs.
5. In an extra-large mixing bowl, fold whipped cream into pastry cream; set aside.
6. Line the bottom of a 9x13" baking dish with ⅓ of the graham crackers, breaking them in half if needed to completely cover the bottom of the pan.
7. Scoop ½ of the cream filling on top of the grahams; spread evenly.
8. Repeat with another layer of grahams and filling.
9. Top filling with a third layer of grahams.
10. Spread icing evenly over the top layer of grahams.
11. Loosely cover cake with plastic wrap; refrigerate for 6-12 hrs. or freeze for 12-18 hrs.
12. If frozen, remove cake from freezer and let stand for 10 min. before slicing.
13. Serve immediately or let slices stand at room temperature for up to 1 hr. to soften.

Tasty Tips:

• Use the leftover egg whites in this recipe to make Individual Meringue Shells, a perfect vehicle for your favorite summer fruits.
• This recipe will hold best if you stabilize the whipped cream. To do this, sprinkle 1 tsp. unflavored gelatin over 1 tbsp. cold water in a small microwave-safe dish. Let stand for 1 min., then microwave for 8-10 sec. While making the whipped cream, whisk in sugar just before soft peaks form, then drizzle in melted gelatin before finishing whipping the cream.