Bottom Layer: Combine first amount of butter, first amount of sugar and cocoa to saucepan. Bring slowly to a boil. Stir in egg to thicken. Remove from heat and stir in graham crumbs, coconut and walnuts. Pack very firmly into a greased 9x9" pan. (Do NOT, I repeat, NOT, dump a beaten egg into a pot of boiling liquid. Unless you like scrambled eggs in your pastry. Instead, beat the egg in a small bowl and then add a tablespoon or two of the cocoa mixture to the egg and whisk well, then add the egg mixture into the chocolate mix and stir. Also, once this mixture is in the pan, chill it for about half an hour before making the middle layer - this will prevent the bottom layer from blending with the frosting and making it all lumpy.).
Middle Layer: Combine second amount of butter, milk, flavouring and icing sugar in a bowl. Beat together well. Tint a pretty shade of green. Spread over first layer. (Regular Nanaimo bars call for the same amounts of milk, butter and sugar, but omit the [liquid] colouring and flavouring, and have the addition of 2 tablespoons of vanilla custard powder. This means that the mint filling is considerably softer than the regular. To prevent this, add an additional 1/4 cup of icing sugar, otherwise this layer may never firm up and will squish and ooze when the squares are cut. And as with the first layer, chill this before you add the top layer or the mint layer will melt and blend with the chocolate topping.).
Top layer: Melt chips and third amount of butter in a saucepan over low heat. Spread over second layer. Chill and store in refrigerator. (This amount of chocolate IN NO WAY makes enough to properly cover a 9" square pan. It creates a thin, miserly little layer that doesn't look anything at all like the amount there should be based on the accompanying photographs. I'd go for a cup of chocolate, possibly double the original amount. Also - let the chocolate firm up at room temperature and cut as soon as it's firm. If you chill this first, and then try to cut it, the chocolate will get hard and crack and you'll have an ugly ol' mess like I did.).