Try mixing white wine vinegar, fresh lemon juice, butter and tarragon in a pan, warm through and serve over meat.
You can stir in a mustard like dijon too, add garlic, add olive oil - no real hard and fast rules with this sort of thing. Make a cream sauce with a little oil, cream, tarrgon, pepper, garlic and white wine vinegar all blended.
Make a marinade as well - mix up olive oil, fresh tarragon, mustard powder, salt. pepper, lemon juice, white wine and garlic. Combine it all and pour over meat. Leave as long as possible to marinade.