Preheat oven to 350 degrees F. Spray two 9 inch round cake pans with sides THAT ARE AT LEAST 2 inches high, with flour-added baking spray.
Combine all ingredients in a large mixing bowl and stir to mix. With an electric mixer, beat for a full minute, scraping sides of bowl well.
Divide batter evenly among pans (if you have a scale, you should weigh about 25 oz in each pan).
Bake for 30 minutes on center rack or until cakes test done. Let cool in pans for 10 minutes, then carefully invert. Let cool completely.
To make the frosting, beat the softened butter and 1 cup of sugar until smooth. Continue adding sugar gradually until you've used all 4 cups, then beat in the salt and vanilla. Add the milk 1 tablespoon a time, beating until smooth and creamy. If you feel like the icing is too creamy, add a little more sugar. If it is too dry, add more milk.
Note: I used White Lily and it worked perfectly, but any all-purpose flour should be fine.