Cut 5 of the garlic cloves in half lengthwise, thin thinly slice them.
Make slits in the lamb and insert the garlic slices into the meat.
Coarsely chop the remaining 7 cloves.
In a small dish, combine the chopped garlic, rosemary, thyme, pepper, and oil.
Mix well; then rub mixture over the lamb; cover and refrigerate 1 hour.
Preheat oven to 375°; lightly oil a large roasting pan.
About 20 minutes before roasting, remove the lamb from the refrigerator; season it with salt.
Put the lamb in the roasting pan; roast for about 1 ½ hours, or until an instant-read thermometer inserted in the thickest part reads 134°.
Begin checking the temperature after 1 hour and 10 minutes, keeping in mind that lamb will cook quickly once it reaches a temperature of 125°.
Transfer lamb to a serving platter and let it rest, loosely covered, with foil, for 30 minutes.
Remove the pan juices in the roasting pan to make the jus.
Make the potatoes: peel the potatoes and as each one is peeled, drop it into a bowl filled with cold water.
Slice the potatoes ½ inch thick and return them to the water to prevent discoloring.
In a 12-inch saute pan, heat the oil over med-high heat; cook the onions, stirring, for about 6 minutes, until softened.
Add in the garlic and cook, stirring, for about 2 minutes, until softened.
Drain the potatoes and add them in to the pan along with the parsley, thyme, and rosemary; season with salt and pepper, and cook for 10-12 minutes, until the potatoes and onions begin to brown lightly.
Add in 1 cup of stock, stir well, and cook for 4-5 minutes, until the stock reduces a little.
Add in the remaining ¾ cup stock and cook, tossing the potatoes and onions, for about 18 minutes, until the potatoes are tender when pierced with the tip of a sharp knife but still hold their shape and the stock has reduced to a thick, flavorful glaze; set aside, covered, to keep warm.
Make the haricots verts: in a big saucepan of boiling water, cook the beans for about 4 minutes, until tender but still firm; drain and toss with the butter and season with salt and pepper; set aside, covered, to keep warm.
Make the jus: pour off all but 1 tablespoon of fat from the lamb roasting pan.
Set the pan on the stove, covering 2 burners.
Add in the shallot and cook, stirring, for about 2 minutes, taking care not to let it burn.
Add in the wine; bring to a boil.
Deglaze the pan, using a wooden spoon to scrape up the browned bits sticking to the bottom; transfer the contents of the pan to a saucepan.
Set the saucepan over high heat and boil for about 8 minutes, until the wine nearly evaporates.
Add in the stock and the collected juices from the resting lamb and return to the boil, skimming any foam that rises to the surface.
Cook for about 12 minutes, until the sauce thickens; season with salt and pepper.
Strain the sauce, if desired, and swirl in the butter; should have about 1 cup sauce.
Carve the lamb and arrange the slices on a platter; spoon the potatoes and beans into bowls and serve alongside the lamb; pass the sauce in a sauceboat.
Suggested to serve this with a young French red Burgundy, an aged Bourdeaux, or an Italian Barolo.