Leftovers can be stored in an airtight container for up to 5 days. I suggest keeping the sauce separate from the noodles to avoid mushiness. You can reheat in the microwave or in a saucepan.  To freeze ground beef stroganoff, make the recipe without the sour cream added. Freeze in an airtight container for up to 4 months. Allow to thaw before serving. Reheat on the stove, adding sour cream in before serving.