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1
Let the lamb sit at room temperature for 1 hour.
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2
Heat the oven to 475 degrees F and arrange a rack in the middle.
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3
Meanwhile, prepare the braising liquid.
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4
Place the wine, broth, honey, mustard, zest, and juice in a medium saucepan over medium heat and whisk to combine.
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5
Cook, stirring occasionally, until the honey has dissolved into the liquid, about 10 minutes.
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6
Remove from heat and set aside.
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7
Combine the measured salt and pepper and the coriander in a small bowl.
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8
Rub the lamb all over with the olive oil, then evenly rub it all over with the coriander mixture.
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9
Place the lamb fat-side up in a large roasting pan and roast until the surface is browned all over, about 30 minutes.
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10
Remove the lamb from the oven and reduce the heat to 350 degrees F. Pour the braising liquid into the pan and add the garlic heads cut-side down.
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11
Scatter the rosemary, fennel, and onion around the pan and carefully cover tightly with foil (you will probably need two overlapping pieces).
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12
Return the lamb to the oven and braise until the meat is very tender and pulls away easily from the bone, about 2 1/2 hours.
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13
Remove the foil and return the lamb to the oven until its deeply browned all over and the pan juices are bubbling, about 30 minutes more.
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14
Remove the lamb to a cutting board and cover loosely with foil.
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15
Set a fine-mesh strainer over a medium saucepan and strain the braising liquid, pressing on the solids; discard the solids.
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16
Using a large spoon, skim and discard the excess fat from the surface of the braising liquid (alternatively, you can use a fat separator).
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17
Heat the braising liquid over medium-high heat until boiling.
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18
Continue boiling until reduced to about 1 1/2 cups, about 25 minutes.
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19
Taste and season with salt and pepper if necessary.
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20
Carve the lamb and serve with the sauce.
