Place steak in a glass or ceramic pan. Score top of steak with a sharp knife in a criss-cross pattern to allow marinade to penetrate. Whisk together all ingredients except tarragon. Pour marinade over steak. Sprinkle tarragon over top. Cover and marinate in fridge 2 hrs to over night.
Remove steak, season with salt & pepper. Discard marinade. Cook over med-high grill. Enjoy!