Step 1Heat the oven to 350 degrees. Thickly butter the bottom of a 9-inch square baking dish.
Step 2In a metal bowl set over a saucepan of simmering water, combine the chocolate and 4 tablespoons butter, stirring occasionally, until both are melted. Stir in the sugar, egg and vanilla and blend well. Add one-third cup flour and one-half teaspoon of the salt and mix well. Scrape into the prepared pan and smooth the top.
Step 3For the topping: Melt the remaining 4 tablespoons butter. Add the brown sugar and the remaining one-fourth teaspoon salt and mix well. Stir in the egg yolk and vanilla and mix well. Combine one-fourth cup flour and baking soda and stir into the batter. Blend in the coconut and pecans. Drop the topping evenly over the prepared base to cover it.
Step 4Bake 20 to 25 minutes, until the topping is well browned. Cool on a rack before cutting into squares. (If you cover the pan for at least 4 hours or overnight, the brownies will be more gooey and easier to cut.)