Preheat the oven to 375 degrees.
In a large bowl, cream together the butter and sugar.
Add the buttermilk and baking soda. Mix well.
Add in the flour and vanilla. Mix until combined.
Bake at 375 degrees for 30 minutes or until the center bounces back when you touch it.
While the cake is baking, make the topping. In a bowl, combine the butter, milk, brown sugar and nuts. Mix well.
Spread this mixture all over the top of the warm cake.
Place under the broiler (turned to low) and bake for 1-3 minutes or until the nut topping is bubbling.
Remove from the oven and allow the cake to cool.
Serve warm alone, with whipped cream or with ice cream.