Let's see. I'd say prep up by making a bouquet garni (parsley stems, peppercorns, bay leaf, and fresh thyme wrapped in cheesecloth for the traditional, I'd say some marjoram and a pinch of oregano probably wouldn't hurt), slice the leek and soak it in a water bath to wash out the sand, dice your potatoes and some raw bacon.
Put a little fat in your soup-cookin' pot over low heat, and add the bacon. Render off the bacon fat. Throw in the leeks and maybe some minced garlic or diced celery, and saute them until they're a tender. Add a splash of white wine, let that boil down for a bit, then add some milk/cream, chicken stock, and the bouqet. Bring it up to a boil -- be careful, milk expands to about eighteen times its normal volume when it boils, so depending on how much dairy you have in your soup you may need to watch it -- drop to a simmer, and let it cook until the potatoes are tender.
Bowl, sprinkle on some minced parsley, and eat.
This has been the largely unhelpful "cooks don't measure a goddamn thing" potato-leek soup recipe, from off the top of my head. I'm probably forgetting some vital part of proper potato soupery and will be fiercely chastised by everyone else.
If you're itching to try out your new roasting pan, braised leeks are pretty fantastic, and would go quite nicely with a marinated and grilled/pan-seared chicken breast and some fried potatoes sprinkled with minced parsley. I'd give you a marinade recipe but I improvise every one I make -- a little oil, a little acid (wine is probably a better choice here than, say, citrus juice), some salt and pepper and herbs. To braise the leeks, saute them briefly in the roasting pan, half-cover them with liquid (stock, or wine again), and put them in a 300F or so oven until they're super-tender.
For serious potato frying, slice the potatoes the night before and let them soak in water overnight. Or for a technique I've heard of but not actually tried myself, cut them into shape and fry them in oil until they just start to blister, then pull them out of the oil and freeze them overnight. Then take them straight out of the freezer and drop them into the hot oil to fry the rest of the way when you're cooking dinner.
Either way, copious salt and minced parsley as soon as they're done.
