Preheat oven to 350. Cream butter and sugar with electric mixer until light and fluffy about 3 minutes. Add eggs and vanilla and mix in well. Add cocoa powder, salt and flour and stir until well combined. Grease a 8" pie plate with butter or Pam. Pour mixture in pie plate. Bake for 30 -35 minutes until center is set. If you like , you can dust with powdered sugar and serve with a side of whipped cream or vanilla ice cream!