Cream the butter and brown sugar together
in a bowl until light and fluffy,
using an electric mixer at medium speed.
Add the eggs, one at a time,
beating well after each addition.
Add the cooled chocolate, coffee powder,
and rum flavoring, blending well.
Stir in the flour and the chopped walnuts
and turn into the unbaked pie shell.
Arrange the walnut halves in a circle
around the edge of the pie.
Bake in a preheated 375 oven for 25 minutes
or until set around the edges.
Cool on a wire rack.