Mustard-Horseradish Sauce

I don't always serve a sauce with grilled flank steak, but decided to do so since I had some fresh tarragon in the fridge. This sauce worked well with beef but would be good with salmon, shrimp or chicken.

2/3 cup sour cream
1/4 cup Dijon mustard
2 T chopped fresh tarragon
2 T olive oil
2 T prepared white horseradish

Mix all together and chill well.