I'm going to use a thermometer to 130F, but do you have a rough cooking time for planning purposes? I have a leg that's closer to 9lbs in size. Thanks.
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That is a large leg of lamb! I usually have a 4-5 pound leg and if it's pretty even in size I plan for 12-15 minutes per pound.
And that's the minimum weight! http://purebredlamb.com/butcher-shop/leg-of-lamb/
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It's really hard to give more than a guesstimate, c4f, because everyone's oven is different. It's been a long while since I've done this recipe with a leg that large, so I don't remember. But in any case, everything goes so speedily in my convection oven that if I roasted by time, overcooking would become "normal!" I highly recommend a digital probe thermometer.
The last time I did a 5-pound with this recipe, it was done in under 40 minutes.
WOW! that's some lamb. This farmer brings his lamb to the Union Square Greenmarket. I buy from him: http://www.catskill-merino.com/content/157