Preheat oven to 350 degrees. With an electric mixer, beat butter and cream cheese until smooth. Add sugar; beat until light and fluffy, about 5 minutes. Add eggs, one at a time, beating well after each addition. Mix in vanilla. With mixer on low, add flour and salt in two additions, beating until just combined.
Generously coat two 8 1/2-by-4 1/2- by-2 1/2-inch loaf pans (1 1/2 quarts each) with cooking spray; immediately pour in batter (pan will seem full). Tap pans on work surface to eliminate any large air bubbles.
Bake until golden and a toothpick inserted in the centers comes out almost clean, 60 to 75 minutes (if the tops begin to brown too quickly, tent with aluminum foil).
Cool 10 minutes in the pan. Turn out the cakes; cool completely, with top sides up, on a wire rack.
You can also bake the batter in a 4-quart tube or Bundt pan. Increase the cooking time by about 5 minutes.