Preheat oven to 350º F.
In medium bowl, combine flour, baking soda and salt. In large bowl, beat butter and sugar with electric mixer until light and fluffy. Beat in egg and vanilla. Blend in melted chocolate; mix well. Add flour mixture to butter mixture, mixing until incorporated. Stir in white chocolate chips and walnuts. Drop by mounded tablespoonfuls about 2-inches apart onto ungreased cookie pan.
Bake 10-12 minutes or until edges are set (centers will be soft). Cool in pan on cooling grid 1 minute. Remove from pan; cool on grid.