1Place roast on a 18x11 inch piece of heavy-duty aluminum foil.
2Stir together mustard and next 4 ingredients; spread over roast.
3Fold foil over roast to seal.
4Place in shallow roasting pan, and chill at least 8 hours.
5Remove roast from foil; place in roasting pan. Let roast come to room temperature.
6Bake covered, at 450 for 20 minutes.
7Arrange uncooked potatoes (seasoned with 2 tablespoons olive oil, 2 garlic cloves pressed, 1 teaspoon salt and 1/2 teaspoon pepper sage and rosemary to taste cut into wedges) around roast, if using add pearl onions on top of potatoes and bake, uncovered, 25 more minutes or until potatoes are tender and roast is done.
8Remove from oven; cover and let stand 15 minutes before slicing.
9Garnish, if desired with rosemary or other herb of your choice.