Sift together flour, cocoa, baking powder, baking soda, and sugar. Make a well in center of sifted dry ingredients. In a separate bowl mix buttermilk, oil, egg yolks, and vanilla. Pour into the well and mix with dry ingredients.
Beat egg whites with cream of tartar until soft peaks form. Gradually fold into batter, one third at a time. Fold in pecans (if used). Cook in waffle iron according to manufacturer's instructions. Top with ice cream.