Sift together the first three ingredients.
Mix shortening, sugar, and eggs in a bowl until light and fluffy.
Add half of the flour mixture and beat well. Mix in ¼ cup PET milk, water, and 1 tsp vanilla. Add the rest of the flour mixture and beat well.
Divide batter. To one bowl of batter, and chocolate batter ingredients. To the other bowl, add the chocolate chips.
Spread chocolate batter evenly in a greased 13x9 pan and arrange graham crackers on top.
Drop tablespoons of vanilla batter onto graham gracker layer. Spread evenly to form a third layer.
Bake in a 375-degree oven for 30 mins (*note: Start checking after 20 mins! Mine cooked fast!).
Cool and cut into 3 dozen bars.