Melt 1 cup chocolate chips and butter in large, heavy saucepan over low heat. Stir until smooth. Remove from heat. Add eggs, stir well.
Add flour, sugar, baking soda and vanilla; stir well. Stir in remaining 1 cup chocolate chips and nuts.
Spread into greased 9x13-inch baking pan. Bake in preheated 350 degree oven for 18 to 22 minutes or until wooden pick inserted in the middle comes out still slightly sticky. Cool completely. Cut into 2-inch squares. Makes 2 dozen.