1. Preheat oven to 350F.
2. In a medium saucepan, melt butter.
3. Stir in chocolate and remove from heat to cool.
4. In a small bowl, beat eggs and vanilla and gradually add sugar, beating constantly.
5. Add chocolate mixture until well blended.
6. Slowly stir in flour and nuts.
7. Turn out into a greased 8-inch pan and bake for half hour.
8. Allow to cool and cut into 2-inch squares.