1. Preheat oven to 325°F (165°C).
2. Mix the oil and the sugar together. Add the rest of the ingredients in the order listed. Mix very well until all the ingredients are combined.
3. Pour into an eight-inch (20-centimeter) square baking pan and bake for 25 minutes or until the center is just setting. Remove from oven and let cool.
4. Remove the ice cream from the freezer and let stand for about 20 minutes or until softened. Pour into a large bowl or a foil pan. Cut up the brownies into small chunks and mix into the ice cream. Flatten the top with a spoon and refreeze until a few minutes before ready to use.
5. For the walnuts, pour sugar and walnut pieces into a thick-bottomed pan. Let sugar melt over low heat, stirring constantly until the sugar coats the walnuts. Let cool completely.
6. To serve, scoop out the ice cream and top with crushed Viennese crunch or caramelized walnuts.