Beat butter and brown sugar at medium speed with an electric mixer until light and fluffy. Add eggs, 1 at a time, beating after each addition. Stir in melted chocolate, coffee granules, and vanilla. Stir in flour and walnuts. Pour into pastry shell.
Bake at 375° for 25 minutes; cool completely. Chill.
Love this recipe - have made it MANY times and everyone thinks it's great!