In med size sauce pan on medium temp, melt the chocolate squares and butter, stirring occasionally with a whisk. REMOVE from heat when thoroughly melted.
Gradually add sugar, whisk together
Mix eggs/vanilla in a bowl before gradually adding to the melted chocolate mixture. Whisk together thoroughly.
Gradually, add flour. Whisk together thoroughly.
Fold in the chocolate chips and nuts. Pour into a well buttered 9" X 13" baking pan. Bake at 350 for 25 to 30 min. Do not over cook.
Optional: For a fancy look, you can drizzle melted white chocolate chips over the top...after they have cooled!