Preheat oven to 375 degrees F. Line a cookie sheet or jellyroll pan with parchment paper. Set aside.
Place the butter, Splenda Granulated Sweetener, sugar, vanilla and salt in a medium mixing bowl. Mix, using the paddle attachment of an electric mixer until the mixture is light and creamy (approx. 1-1 1/2 minutes). Add cocoa powder and all the flour. Mix until just blended.
Remove dough from bowl and form into a ball. Place the ball of dough on the parchment lined pan. Roll the dough into a rectangle approx. 6 1/2 inches wide by 11 inches long and 1/4 inch thick. Pierce the surface of the dough with a fork all over. This allows the air to escape during baking preventing air pockets from forming.
Bake in preheated 375 degrees F oven 20-25 minutes, rotating the pan after 10 minutes of baking. Remove shortbread from oven after 20-25 minutes and immediately cut into 24 fingers or rectangles while the shortbread is still warm. If allowed to cool, shortbread will not slice well.