Cream butter; gradually add sugar, beating at low speed of an electric mixer until light and fluffy.
Add egg yolks, beating well.
Place chocolate in top of a double boiler; bring water to a boil.
Reduce heat to low and cook until chocolate melts.
Gradually add chocolate to creamed mixture, beating constantly; stir in 1/2 cup pecans, and fold in egg whites.
Press 1 cup cookie crumbs into bottom of an 8-inch square dish; spread chocolate mixture over crumbs.
Chill until firm.
Combine candy, marshmallows, remaining 1/2 cup pecans, and 1/2 cup cookie crumbs; stir well.
Gently stir in whipped cream.
Spread whipped cream mixture over chocolate layer; sprinkle remaining 1/2 cup cookie crumbs over top.
Chill.