Whisk 1/4 cup each whole-grain mustard and olive oil, 3 tablespoons dijon mustard, 1 small minced shallot and 1 tablespoon chopped tarragon in a bowl. Whisk in 2 to 3 tablespoons water and season with salt and pepper. Serve on grilled steak.
TIP: Switch up the tarragon with whatever herbs you have on hand. This sauce is great as a burger topping, too!