Preheat the oven to 350 degrees F.
Butter and lightly flour an 8-cup loaf pan (10 by 5 by 3), knocking out the excess flour.
Into a large bowl, sift the flour, cocoa, baking soda and salt.
In a small bowl, whisk together the buttermilk, molasses, and vanilla.
In a large bowl with an electric mixer, cream together the butter and sugar, beating about 3 minutes. Add the eggs 1 at a time, beating well after the addition of each. Alternating, add the wet and dry ingredients in 3 additions each, mixing just until combined and being careful not to overwork.
Pour into the prepared pan and bake until the cake is risen and just set and a tester inserted into the middle comes out clean, 50 to 55 minutes. (If cake gets too brown, tent it with foil).
Cool in the pan 40 minutes, then turn out onto a wire rack to finish cooling. Slice cake into pieces, top with pecan topping, and serve with vanilla ice cream, if desired.
Yield: 8 servings
In a saucepan, combine the ingredients, and simmer until thick. Serve over top of cake.