Melt Chocolate and butter together in a small saucepan over low heat. In a large bowl, mix sugar, flour, eggs and vanilla. Add melted chocolate mixture and mix well. Stir in nuts and chocolate chips. Pour into greased 9x13-inch pan. Bake at 180ºC or 30 to 32 minutes. Test corners to see if done, as center will seem gooey. Cool 30 minutes. refrigerate for 1.5 to 2 hours. Cut into squares.