In a large mixing bowl, beat sugar and 1 cup butter until light and fluffy.
Add eggs one at a time, beating well after each addition. Add sour cream, and vanilla. Mix well.
In a smaller bowl, combine flour, baking powder, and salt. Add to butter mixture alternating with milk, beginning and ending with flour mixture. Beat on low until just combined after each addition.
Pour batter evenly into three standard greased and floured 9 inch round cake pans or two deep 9 inch round cake pans(2 inches deep or more).
Bake at 350 degrees for 30-40 minutes or until inserted toothpick comes out clean.
Cool layers in pans for 10 minutes then turn out onto wire racks to cool completely.
Frosting: In a dutch oven or large saucepan over medium heat, combine remaining 1 cup of butter, brown sugar, evaporated milk, and salt. Mix well.
Cook for 10-12 minutes or until mixture reaches 235 degrees.
Cool slightly and beat with hand mixer until mixture reaches spreading consistency. Frosting will continue to thicken as it cools. If frosting becomes too thick, add a little milk. If frosting is too thin, continue beating.
Quickly spread between layers and on top and sides. Serve at room temperature.