Preheat oven to 350 Fahrenheit, and grease a spring-form pan.
Cream together the butter and sugar. Add eggs and vanilla.
In separate bowl, mix flour, salt, and cocoa powder.
Stir dry ingredients into the wet ingredients. Mix well. It will be a thick batter.
With a flat spatula, spread batter into spring-form pan and bake for 18-20 minutes.
Let cool completely and then freeze for at least 30 minutes.