In a small sauce pan, add the sour cream, butter, sugar and salt. Cook, stirring constantly over low heat until the butter melts. Turn off the heat and allow to the mixture to cool until it's just warmer than lukewarm--about 100 degrees.
Once the sour cream mixture is almost cool enough, add the yeast to the warm water in a small bowl or measuring cup. Allow the yeast to stand until it's foamy--about 5 minutes.
In a medium bowl, add the sour cream mixture, the yeast mixture, the egg and the flour. Stir until a soft dough forms.
Cover the dough with plastic wrap and refrigerate 8 hours.
After 8 hours, punch the dough down in the center and turn out onto a floured surface.
Turn it over on itself three or four times (knead it lightly) to smooth it out a bit. Lightly grease a muffin pan. Then pinch off enough dough and roll balls about the size of a big marble.
Place three balls in each muffin cup, cover with a clean dish towel and allow the dough to rise until doubled in size--about one hour.