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, dust with powdered sugar and serve with a side of whipped cream or vanilla ice cream.