Combine the chocolate, sugar, and water in the top of a double boiler.
Heat and stir over hot water until mixture is slightly thickened and smooth, about 12 minutes.
Blend about 3 tablespoons of the mixture into the egg yolks; immediately stir into mixture in double boiler.
Cook and stir over boiling water 3 to 5 minutes.
Remove from water and blend in the extract.
Set aside to cool.
When mixture is cooled, cream the butter until softened.
Gradually add confectioners' sugar, beating constantly until light and fluffy.
Add the chocolate mixture, a small amount at a time, blending well after each addition.
Beat the egg whites until stiff, not dry, peaks are formed.
Fold into chocolate mixture.
Use enough graham crackers to cover the bottom of a 8x8x2-inch pan.
Spread one third of the chocolate mixture over crackers.
Add a second layer of crackers and spread with remaining chocolate mixture.
Repeat layering and top with graham crackers.
Cover and chill about 48 hours.