Stir yeast into warm water to dissolve. Mix butter, sugar and egg well. Stir until sugar dissolves and add to yeast mixture. Stir in flour until well mixed. Put in air-tight container and refrigerate for at least 2 hours. Bake in greased muffin tins 2/3 full at 350 degrees for 20 minutes. This will keep in the refrigerator for up to 2 months if kept tightly closed.