In a medium saucepan over medium heat, bring beer, covered, to a boil.

Meanwhile, in a bowl, beat together egg yolks, sour cream, cornstarch, sugar and salt until well blended. Transfer mixture to a large saucepan over low heat. Pour in hot beer, a little at a time, stirring until well combined. Do not boil.

To serve, divide bread cubes into four warmed soup bowls. Sprinkle cheese over bread. Pour hot soup over all and serve piping hot.