While the grill is preheating combine the flour, cocoa powder, salt, baking soda, and granulated sugar in a medium bowl. Stir with a whisk to blend.
Combine the buttermilk, egg, melted butter and vanilla. Whisk to combine. Add the buttermilk/egg mixture to the dry ingredients and stir until just blended. Do not over-mix.
Using a ¼-cup measure, drop batter onto the preheated griddle plates. Cook cakes until bubbles form on the surface, about 3 to 4 minutes; flip and cook until done, about 3 ½ minutes longer.