Step 1

In a large bowl, whip the chilled heavy cream with 1/2 cup powdered sugar and 1 teaspoon vanilla extract until stiff peaks form. Set aside.

Step 2

In another bowl, mix the sour cream with the remaining 1/2 cup powdered sugar and 1 teaspoon vanilla extract. Gently fold the whipped cream into the sour cream mixture until combined. Add more sugar if you have a sweeter taste preference.

Step 3

Spread about 1 1/2 cups of the frosting to cover the bottom of a 9 X 13 inch pan. Top with a layer of graham crackers, breaking the crackers as necessary, so the crackers fit like a puzzle in a single even layer. Top with more frosting, about 2 cups (it doesn’t have to be exact), spreading the frosting to cover the graham crackers.

Step 4

You should have these layers in the end: 1 1/2 cups frosting, graham crackers, 2 cups frosting, graham crackers, 2 cups frosting, graham crackers, remaining frosting.

Step 5

Grate a chocolate bar on top of the last layer of frosting.

Step 6

Chill the cake in the refrigerator for at least 6 hours, or overnight before serving. You can make the cake up to 2 days in advance.