Preheat oven to 350. Spray your 13x9 dish and set aside. Cake-cream the butter and granulated sugar until fluffy. Add the eggs, one at a time, mixing well after each addition. In a medium bowl sift the flour, salt, and baking soda together.
Alternately add flour mixture and sour cream to the batter and blend. Stir in vanilla. Pour the batter into the prepared 13x9 and bake 45 minutes or until cake tests done in center. Remove from oven and let cool.
Make the icing-In a large saucepan, combine the butter, brown sugar and milk. Cook over low heat until butter melts. Increase the heat to medium and cook 2 minutes longer. Remove from heat and stir in vanilla. Slowly add your powdered sugar mix well and frost the cooled cake.