Cream butter and sugar until light and fluffy. Beat in eggs and vanilla. In another bowl, whisk flour and salt; gradually beat into creamed mixture. Add chocolate chips and, if desired, walnuts; mix well. Divide dough in half. Shape each into a disk; wrap in plastic. Refrigerate until firm enough to roll, about 30 minutes., Preheat oven to 325°. On a lightly floured surface, roll each portion of dough to 1/4-in. thickness. Cut with a floured 2-in. triangle-shaped cookie cutter. Place 2 in. apart on ungreased baking sheets. Bake until edges begin to brown, 10-12 minutes. Cool on pans 2 minutes. Remove to wire racks to cool completely., Meanwhile, in a microwave, melt white baking chips; stir until smooth. Dip cookie tops in melted chips; sprinkle with nonpareils. Let stand until set.