I loooove a good jus. And I agree with the comment on it going well with beans. To avoid the falling apart, consider serving it in a little sauce boat? That is often how jus is served in dinners in France, especially when meals aren't plated but served family style. I don't know how many guests you'll have but you could have one or two of them, or if you want to do individual plating you could consider adding a little cup of jus inside each plate, or to the side of each plate. Just make sure you warm the cups beforehand so the jus stays hot and doesn't gel.
How are you going to make your jus?
And what wine are you serving with that!?
And how do you cook your beans? I like to pressure cook my beans with a bay leaf and some unpeeled garlic cloves. Then I render a bit of duck fat (or pork or chicken fat) and sweat some finely diced onions and a carrot, once sweated I add a bit of tomato paste and cook for a few minutes, add the cooked beans and a tablespoon of flour to thicken, cook the flour so it binds with the remaining duck fat and then add a laddle or two of the bean's cooking liquid, and cook that for a few hours in a clay pot in a medium oven, breaking the crust that forms on top every so often to thicken the "sauce" with it.
Anyway sounds delicious.
Excellent point about the sauce/gravy boat. I do have beautiful a Wilton Armetale one that we got as a wedding present. It is normally how I serve jus with our Christmas Prime Rib Roast. I will often do a ramekin of sauce or jus for more casual dinners, but I really want to make this one pretty.
The question of how to make the jus is an interesting question. When I normally make a larger roast that cooks a long time, I will fill the bottom of the roasting pan with aromatics vegetables and herbs, pre-browned trimmings from the roast, and red wine and basically let that braise together while the roast cooks.
I know, it doesn't fit the usual pattern of letting the drippings glaze on the bottom with the vegetables and then deglazing with red wine or stock when done. However, it works extremely well when I do a big, long roast like a prime rib of beef. I buy my rib primals whole and dry age them myself at home, so I have a lot of tough cap meat left over when I trim it. The dry-aged cap makes for a beautiful base for the jus, which I brown in the roasting pan with the aromatics before I add the roast on its rack. I am basically deglazing the pan before I even put the roast in the oven. It also frees up the roasting pan to use to sear the roast at the end and to render fat for Yorkshire puddings.
With the lamb, since this is a young lamb and the leg is quite small, I don't think I can use my usual technique. I am thinking of either making a lamb jus or a red wine jus from Thomas Keller's Bouchon cookbook. The former is basically an accelerated stock making process using browned bones, aromatics, and herbs. With repeated glazing and deglazing. The "quick lamb sauce" from The French Laundry Cookbook that I used to make my Cepes Bordelaise sauce for the rack of lamb is very similar and produces phenomenal results every time. The red wine jus recipe seems to involve reducing red wine, aromatics, and herbs to a glaze and then reconstituting with stock and reducing to a jus. I'm torn between the two jus recipes. So I am thinking of making the red wine jus, but making the lamb jus and substituting it for the veal stock in the red wine jus recipe. Overdone? Maybe, but I have a feeling it will be really, really good.
My beans recipe is pretty simple, I just use the one from The French Laundry Cookbook. Soak the beans overnight. Rinse, bring to a simmer, then rinse again. Then slowly simmer in a combo of water and chicken stock with large chunks of carrot, onion, leeks, and garlic as aromatics until tender. I have modified the recipe for my own taste by adding the rind from a chunk of double smoked bacon to my aromatics. I find it slowly releases enough salt into the pot over the cook to allow seasoning to penetrate into the beans. When the beans are done, I drain them and warm them with a little jus or quick sauce from the accompanying protein. So in this case, I would reserve some of the lamb jus to use just for the beans. Then I would fold in a little cold butter to increase their creaminess and salt and pepper to taste with some fresh thyme leaves or something for colour as well as some crispy double smoked bacon lardons.
For the wine, since the lamb recipe is bordelaise and in particular for Pauillac lamb, I am going see what I have in the cellar for a nice Cab-dominant Left Bank red. Something with some age on it to soften it up to match the subtle flavours from long roasting with herbs.