Preheat oven to 375 degrees.
Beat together butter and vanilla.
Beat in sugar until mixed well.
Beat in flour until mixed well.
Stir in chocolate chips.
Press into an ungreased 8X8 or 9X9 square cake pan.
Sprinkle with chopped nuts, if using. Or sprinkle with more chocolate chips.
Bake for 25 minutes.
Cool and then break into pieces or use a pizza cutter to cut into pieces.