Preheat oven to 350°F (175°C).

Make sour milk by adding soda to milk and stirring to dissolve.

In a large bowl, combine sugar and cocoa.

Add oil and egg, stir well.

Combine salt and flour in a separate bowl.

Add the dry ingredients alternately with the sour milk mixture to the wet ingredients, mixing well after each addition.

Add vanilla extract.

Pour batter into greased and floured layer pans or a sheet cake pan.

Bake for 30-40 minutes, or until a wooden skewer inserted into the center comes out clean.

While the cake is baking, prepare the icing.

In a saucepan, combine butter, Coca-Cola, and cocoa.

Heat to boiling point, then remove from heat.

Add confectioner's sugar and chopped nuts.

Beat well until smooth.

Once the cake has cooled slightly, spread the icing evenly over the top.