Melt chocolate in top of large double boiler or mixing bowl over hot water.  Remove from water and mix in oil and sugar.  Add eggs one at a time and beat well after each.  Add vanilla and mix well.  Sift flour, baking powder and salt together.  Stir into chocolate mixture.  Fold in nuts if using.  Dough will be very soft.  Cover bowl of dough and chill in the refrigerator. When mixture is cold, roll by spoonfuls into small round balls.  Roll in powdered sugar and baked on greased cookie sheet @ 350 for 10 to 12 minutes.  Tops of cookies will look damp.