In a medium saucepan over low heat, melt the butter.
Add the sugar and cocoa powder and gradually beat in egg.
Cook, stirring, until the mixture thickens (about 1-2 minutes).
Remove from heat and stir in vanilla extract, graham cracker crumbs, coconut, and chopped nuts.
Press mixture evenly into prepared pan. Cover and refrigerate about 1 hour, or until firm.
For the Filling:
In a large bowl, cream butter. Beat in remaining filling ingredients. If the mixture is too thick to spread, add a little more milk or cream. Spread filling over bottom layer as evenly as you can.
Cover and refrigerate until firm, about ½ hour.
For the Topping:
In the top of a double boiler over simmering water, melt the chocolate and butter. Spread over the cooled filling. Refrigerate until firm, about ½ hour.
To Serve:
To prevent the chocolate from cracking, let the pan of nanaimo bars sit at room temperature for 10-15 minutes. Cut into 25 squares with a sharp knife.
Recipe by Kiku Corner at https://www.kikucorner.com/2015/03/07/nanaimo-bars/