Remove the lamb from the refrigerator and unroll it on the cutting board. With a sharp knife trim off the excess fat and any gristle. 

To make the lamb the same thickness, butterfly-book the thick parts by making shallow diagonal slices and pressing the slices open like pages in a book. 

Then lightly score the the meat in a 1-inch crosshatch. Place the lamb on an oil-sprayed wire rack set over a rimmed baking sheet.

To a small dish add the mashed anchovies, and the chopped garlic, mint and rosemary. Stir in the salt and olive oil. 

Rub the herb mixture over the prepared lamb, working the mixture into all the cuts and crevices. Let the lamb rest for an hour on the counter top to come to room temperature and absorb the herb flavor. 

Preheat the oven to 425°F Transfer the baking sheet with lamb still on the wire rack and roast the lamb for 25-35 minutes, depending on desired doneness. For medium-rare an instant-read thermometer will register 125 to 130°F

Let the lamb rest for 10 minutes before serving.