Prepare the Pan and Preheat Oven - Spray the 10-inch loaf pan with cooking spray and sprinkle it with flour. Preheat the oven to 350 degrees Fahrenheit.
Combine All Ingredients - In a large bowl, combine the box cake mix, water, eggs, cream cheese, sugar, vanilla extract, and vegetable oil. Using an electric mixer, beat the ingredients at low speed for one minute. After one minute of mixing, scrape down the side of the bowl and beat for two minutes at medium speed.
Bake the Cake - Once the mixture is fully combined and smooth, pour it into your prepared cake pan. Bake in the oven for 35-40 minutes, or until golden brown. On a wire rack allow the cake to fully cool.
Make the Glaze (Optional) - In a medium bowl, combine the powdered sugar, butter or margarine, vanilla, and milk or half-and-half. Mix all the ingredients together using a whisk, until fully combined. The texture should be smooth.
If desired, add more milk or half-and-half to reach to thicken the consistency. Once the cake is fully cooled, drizzle the icing on top.