Combine first 3 ingredients, stirring well. Unroll roast; trim fat. Reroll roast; secure at 1-inch intervals with twine. Cut 10 (1/2-inch-deep) slits in surface of roast; stuff thyme mixture into slits. Sprinkle with 3/4 teaspoon salt and pepper. Brush mustard over roast. Cover and chill 12 hours.
Preheat oven to 425°.
Arrange 3 rosemary sprigs crosswise on the rack of a broiler pan, and top with roast. Arrange 3 additional rosemary sprigs on top of roast. Bake at 425° for 50 minutes or until a thermometer registers 145° (medium-rare) or desired degree of doneness. Discard rosemary. Let roast stand 20 minutes before slicing.
Combine water and broth; add to broiler pan. Cook over medium heat; bring to a boil, scraping pan to loosen browned bits. Cook 4 minutes or until mixture measures 1/2 cup; stir in remaining 1/2 teaspoon salt. Slice roast; serve with sauce.
I used whole grain mustard and whole not ground bay leaves, but followed the recipe to the letter other than that. Cooked the lamb to rare (130) in 40 minutes then let it rest a solid 20-30 minutes. Loved, loved, loved this lamb; some of the best I've ever had. I will make this again for sure.
This came out very tender and moist. I cooked mine longer since my husband prefers it more well done. I didn't use bay, but used fresh oregano instead. I will definitely use this recipe in the future. I marinated it for about half the time. Still was very good.
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