Preheat oven to 350°F.
Line the bottom and sides of an 8-inch square metal cake pan with one piece of foil, large enough to wrap over the edges of the pan to help removing the cake from the pan when baked. Lightly butter the bottom ad sides. Set aside.
Melt chocolate and butter in a heavy, deep sauce pan over very low heat, stirring a few times until combined and melted. Remove from stove and set aside to cool slightly for 3 or 4 minutes.
Off the heat, stir in the sugar and vanilla. Add the eggs, one at a time, stirring well to combine after each addition.
Add flour and salt and stir well to combine. Stir in the chopped nuts.
Pour into prepared cake pan and spread evenly. Bake in the lower third of oven for 20 to 25 minutes. Do not over bake, since these need to be moist in the center when you take them from the oven.
Cool 5 minutes in the pan. Then remove to a rack to cool completely.
Wrap the entire cake tightly in plastic wrap and freeze.
About 5 minutes before making the sundaes, remove from the freezer. Cut into squares.
Place one brownie in the bottom of a dessert bowl. Top with a scoop of ice cream.
Spoon warm Ginger Chocolate Sauce over the ice cream, letting it drip down on and around the brownied.
Note: These sundaes can also be made with the brownies defrosted or with freshly baked, unfrozen brownies.
Variation: Omit the nuts from the brownies, and sprinkle chopped, crystalized ginger on the top of the sundae.