Combine butter and coffee granules in a small saucepan or skillet. Cook over medium-low heat until butter melts and coffee granules dissolve, stirring occasionally. Remove from heat, and let cool to room temperature (don't let butter resolidify).
Combine butter mixture, sugars, egg, and egg yolk in a large bowl. Beat at medium speed of an electric mixer until blended. Gradually add flour mixture, beating at low speed just until blended. Stir in mega-morsels and walnuts.
Drop dough by heaping tablespoonfuls 2" apart onto ungreased cookie sheets. Bake at 325° for 12 to 14 minutes. Let cool slightly on cookie sheets. Remove to wire racks to cool completely.