Add in additional milk as needed to get thick but pourable consistency.
Pour over the top of cooled bread.
Let icing set before slicing.
Notes
Flour: Properly measuring the flour makes a huge difference in baked goods. To properly measure flour, either weigh it or stir/sift it to break it up. Lightly spoon it into the measuring cup and level.
Vegetable oil: Any neutral oil, like canola, will work.
Sour cream: I've used regular and low-fat sour cream in this recipe. Both have worked well. I don't recommend using fat-free sour cream.